Search

Reduced intensity conditioning (RIC) is fraught with risk for disease relapse. This may be overcome by donor T cell alloreactivity. Reducing the duration of intense immune suppression in the early term following transplantation may create an immunologic environment favoring rapid T cell reconstitution to influence longer term transplant outcomes. Twenty-six patients were adaptively randomized based on donor-derived T cell recovery, between 2 different dosing schedules of mycophenolate mofetil (MMF): MMF for 30 days post-transplant, with filgrastim for cytokine support (MMF30 arm, 11 patients), or MMF for 15 days post-transplant, with sargramostim (MMF15 arm, 15 patients). All patients were treated with anti-thymocyte globulin at a dose of 1.7 mg/kg/day from day - 9 through day -7 and total body irradiation, 450 cGy given in 3 fractions. Patients were well matched between the study arms and underwent HLA matched related and unrelated donor hematopoietic cell transplantation (HCT). The MMF15 arm demonstrated superior T cell recovery in the first month. This difference persisted through the first year for total T cells, T cell subsets and NK cells. T cell repertoire tended to be more diverse in the MMF15 arm. The long term superior immune recovery in the MMF15 arm is consistent with a disproportionate impact of early interventions in HCT. Clinically, shorter course MMF post-transplant was not associated with increased risk of acute or chronic graft vs. host disease (GVHD), and relapse and there was a trend toward improved overall survival in the MMF15 arm. Reducing the duration of intense immunosuppression in the early term and the use of sargramostim following allogeneic HCT is feasible and leads to superior long-term T cell recovery. This regimen should be studied to improve immune recovery in large cohorts of patients undergoing HCT with RIC.

Alloreactivity forms the basis of allogeneic hematopoietic cell transplantation (HCT), with donor derived T cell response to recipient antigens mediating clinical responses either in-part or entirely. These encompass the different manifestations of graft vs. host disease (GVHD), infection risk as well as disease response. Whilst the latter is contingent upon disease biology and thus may be less predictable, the former two are more likely to be directly proportional to the magnitude of donor derived T cell recovery. Herein we explore the quantitative aspects of immune cell recovery following allogeneic HCT and clinical outcomes in two cohorts of HLA matched allograft recipients who received rabbit anti-thymocyte globulin (ATG) on different schedules (days -9 to -7 vs. -3 to -1). Monocyte as well as donor derived T cell (ddCD3) recovery was superior in those given ATG early in their course (days -9/-7). This difference was related to a more rapid rate of ddCD3 recovery, largely driven by CD3+/8+ cells in the first month following transplantation. Early monocyte recovery was associated with later T cell recovery and improved survival. In contrast rapid and early ddCD3 expansion out of proportion to monocyte recovery was associated with a high likelihood of acute GVHD and poor survival. This analytic methodology demonstrates that modelling ‘early-term immune reconstitution' following HCT yields insights that may be useful in management of post-transplant immunosuppression and adaptive cellular therapy to optimize clinical outcomes.

Alloreactivity forms the basis of allogeneic hematopoietic cell transplantation (HCT), with donor derived T cell response to recipient antigens mediating clinical responses either in part or entirely. These encompass the different manifestations of graft vs. host disease (GVHD), infection risk as well as disease response. Whilst the latter is contingent upon disease biology and thus may be less predictable, the former two are more likely to be directly proportional to the magnitude of donor derived T cell recovery. Herein we explore the quantitative aspects of immune cell recovery following allogeneic HCT and clinical outcomes in two cohorts of HLA matched allograft recipients who received rabbit anti-thymocyte globulin (ATG) on different schedules (days -9 to -7 vs. -3 to -1). Monocyte as well as donor derived T cell (ddCD3) recovery was superior in those given ATG early in their course (days -9/-7). This difference was related to a more rapid rate of ddCD3 recovery, largely driven by CD3+/8+ cells in the first month following transplantation. Early monocyte recovery was associated with later T cell recovery, improved survival, and less chronic GVHD. In contrast rapid and early ddCD3 expansion out of proportion to monocyte recovery was associated with a high likelihood of acute GVHD and poor survival. This analytic methodology demonstrates that modelling ‘early-term immune reconstitution’ following HCT yields insights that may be useful in management of post-transplant immunosuppression and adaptive cellular therapy to optimize clinical outcomes.HighlightsATG given early (day -9 to -7) prior to HCT leads to improved survival and non-relapse mortality. Improved monocyte counts as well as donor-derived T cell counts are seen in recipients of early ATG. Improved clinical outcomes are observed in patients with enhanced monocyte and T cell recovery after HCT.

Killer immunoglobulin-like receptor (KIR) and KIR-ligand (KIRL) interactions play an important role in natural killer cell-mediated graft versus leukemia effect (GVL) after hematopoietic cell transplant (HCT) for AML. Accounting for known KIR-KIRL interactions may identify donors with optimal NK cell-mediated alloreactivity and GVL. A retrospective study of 2359 donor-recipient pairs (DRP) who underwent unrelated donor (URD) HCT for AML was performed. KIR-KIRL combinations were determined and associations with clinical outcomes examined. Relapse risk was reduced in DRP with both higher inhibitory KIR-KIRL (iKIR) and missing KIRL (mKIR) scores, with HR 0.86 (P = 0.01) & HR 0.84 (P = 0.02) respectively. The iKIR and mKIR score components were summed to give a maximal inhibitory KIR ligand (IM-KIR) score for each donor, which if it was 5, as opposed to

Killer immunoglobulin-like receptor (KIR) and KIR-ligand (KIRL) interactions play an important role in natural killer cell mediated graft versus leukemia effect (GVL) after hematopoietic stem cell transplant (HCT) for AML. Mathematically accounting for KIR-KIRL interactions may identify donors with optimal NK cell mediated alloreactivity and GVL. In this retrospective study of 2359 donor recipient pairs (DRP) who underwent unrelated donor (URD) HCT for AML, KIR-KIRL interaction scores were determined. Relapse risk was significantly reduced in donor-recipient pairs (DRP) with higher inhibitory KIR-KIRL interaction and missing KIRL (mKIR) scores, with HR=0.86 (P=0.01) & HR=0.84 (P=0.02) respectively. This effect was not observed with activating KIR-KIRL interactions. The inhibitory KIR-KIRL (iKIR) interaction score components were summed to give an inhibitory-missing ligand (IM-KIR) score, which if it was 5 as opposed to HighlightsInhibitory and missing KIR-KIRL interactions, both individually and collectively are predictive of relapse following URD HCT for AML.Amongst 8/8 HLA matched donor recipient pair relapse reduction was observed in those undergoing in vivo T cell depletion with ATG.TRM is increased in patients with greater magnitude of inhibitory and missing KIR-KIRL interactions.

Anti-thymocyte globulin (ATG) mitigates graft vs host disease (GVHD) risk in patients undergoing allogeneic hematopoietic cell transplantation (HCT). Due to T cell depletion there remains a concern that ATG administration may be associated with an increased risk of malignancy, relapse, and infection in recipients of reduced intensity conditioning (RIC). It was hypothesized that ATG infusion early in the course of conditioning will promote rapid immune reconstitution because of lower levels at the time of graft infusion and will thus help to improve clinical outcomes in RIC. Rabbit ATG (Thymoglobulin, Sanofi Aventis) was administered from day (d) -9 to -7 to HLA matched-unrelated (MUD; 5 mg/kg in divided doses) and -related (MRD; 3.5 mg/kg) donor transplant recipients conditioned with Fludarabine and Melphalan (ATG -9 cohort; N=36). Immune reconstitution and clinical outcomes were compared with a historical control group of patients who received the same doses of ATG from d-3 to -1 (ATG -3 cohort; N=28). Standard GVHD prophylaxis with calcineurin inhibitor and antimetabolite was administered, with CMV and EBV monitoring. ATG -9 cohort had more, MUD recipients 80% vs. 64%; myeloid malignancy (AML, MDS, MPD) 83% vs. 35%. Age (56 vs. 57), graft type (97 vs. 92% PBSC) and CD34+cell dose infused (4.8 vs 4.7 E6/KG) were similar. Immune reconstitution was uniformly superior in ATG -9 cohort, with significantly higher absolute monocyte counts (AMC) at d30, 60 and 90 (P Given the relatively low number of patients in each cohort, the effect of immune reconstitution on clinical outcomes was evaluated in the pooled population. Survival was improved in those with AMC and ddCD3+ cell counts >200/µL at d60 (P=0.004 & 0.016 respectively), and in patients with T cell - monocyte vector magnitude > median (577.48/µL) at that time (P= 0.008), as well as in those with a calculated dT/dt > median (1.96 cells/µL/day) at d45 (P=0.047). The latter was also associated with a reduction in relapse rate (P=0.04), as was ddCD8+ cell count >145/µL at d60 (P=0.04). Acute GVHD risk was increased when dT/dt was >median (7.60 cells/µL/day) at d15 (P=0.0095), and correspondingly with T cell - monocyte vector magnitude > median (1033.3/µL) at d30 (P=0.017). In conclusion, this retrospective study demonstrates that equal doses of ATG administered earlier (d -9 to -7 as opposed to d-1 to -3) during conditioning yield more rapid and robust immune reconstitution. Monocyte and ddCD3+ cell recovery kinetics have a favorable impact on survival and relapse risk following HLA matched HCT. Patients at risk for acute GVHD may be identified as early as d15 post HCT by analyzing ddCD3+ cell reconstitution kinetics. Different ATG administration schedules should be studied prospectively with a focus on immune reconstitution kinetics as a determinant of clinical outcomes. Disclosures No relevant conflicts of interest to declare. OffLabel Disclosure: Rabbit anti-thymocyte globulin for GVHD prophylaxis.

Killer immunoglobulin-like receptor (KIR) and KIR-ligand (KIRL) interactions play an important role in natural killer (NK) cell mediated graft versus leukemia effect following hematopoietic cell transplantation (HCT). However, there is considerable heterogeneity in the KIR gene and KIRL content in individuals, making it difficult to estimate the full clinical impact of NK cell reconstitution following HCT. Herein a novel mathematical model designed to quantify these interactions is presented to better assess the influence of NK cell-mediated alloreactivity on transplant outcomes. Ninety-eight HLA matched unrelated donor (URD) HCT recipients were retrospectively studied. The KIR-KIRL interactions were quantified using a system of matrix equations. Unit values were ascribed to each KIR-KIRL interaction and directionality of interactions was denoted by, either a positive (activating) or negative symbol (inhibition); these interactions were then summed. The absolute values of both the missing KIRL as well as inhibitory KIR-KIRL interactions were significantly associated with overall survival and relapse. These score components were initially used to develop a weighted (w-KIR Score) and subsequently a simplified, non-weighted KIR-KIRL interaction scores (IM-KIR Score). Increased w-KIR Score and IM-KIR Score were both predictive of all-cause mortality and relapse; w-KIR score HR of 0.37 (P=0.001) and 0.44 (P=0.044) respectively; IM-KIR score HR of 0.5 (P=0.049) and 0.44 (P=0.002) respectively. IM-KIR score was also associated with NK cell reconstitution post HCT. KIR-KIRL interactions as reflected by the w-KIR and IM-KIR scores influence both relapse risk and survival in recipients of HLA matched URD HCT with hematological malignancies.HighlightsKiller immunoglobulin-like receptor (KIR) – KIR-ligand (KIRL) interactions display a high degree of variability in HLA matched stem cell transplant (SCT) recipients.Individually, the magnitude of inhibitory and missing KIR-KIRL interactions predicts overall survival and relapse risk following SCT.Taken together the known KIR-KIRL interactions also predict clinical outcomes after HLA matched unrelated donor stem cell transplantation.

Killer immunoglobulin-like receptor (KIR) and KIR-ligand (KIRL) interactions play an important role in natural killer cell-mediated graft versus leukemia effect (GVL) after hematopoietic stem cell transplant (HCT) for AML. There is considerable heterogeneity in the KIR gene and KIRL content of individuals, making it difficult to estimate the full clinical impact of NK cell alloreactivity following HCT. Herein, we validate a mathematical model accounting for KIR-KIRL interactions identifying donors with optimal NK cell-mediated alloreactivity and GVL. This retrospective study was performed on de-identified donor and recipient demographic and clinical outcomes data provided by the Center for International Blood and Marrow Transplant Research (CIBMTR). Donor recipient pairs (DRP) who underwent unrelated donor (URD) HCT for early and intermediate AML were included. KIR-KIRL interaction values were assigned as follows; if an inhibitory KIR (iKIR) on the NK cell encounters a ligand on its target, this will give the NK cell an inhibitory signal and this is scored as a single interaction(Figure 1b), as is the case, if there is no ligand for an inhibitory KIR, i.e., missing KIRL (mKIRL) (Figure 1c). Finally, activating KIR (aKIR) interacting with its ligands is similarly scored(Figure 1a). The absolute values of the iKIR and mKIR scores were summed to calculate the composite inhibitory-missing ligand (IM)-KIR score (Figure 1d). The study cohort was comprised of 2365 donor-recipient pairs (DRP) who underwent URD HCT for early or intermediate AML. Mean age was 53 years; 85% of DRPs were high-resolution 8/8 HLA-matched for HLA-A, -B, -C, and -DRB1. All patients received T cell replete grafts; 42% (n=996) received in vivo T cell depletion, 937 (94%) with anti-thymocyte globulin (ATG); 86% received a graft of mobilized peripheral blood stem cells (PBSC), 59% received myeloablative conditioning. This cohort was primarily of Caucasian descent (89%). When adjusted for recipient age, donor age, CMV status, KPS, GVHD prophylaxis, cytogenetics, disease status, conditioning regimen, in vivo T cell depletion, graft source, and sex match, relapse risk was significantly reduced in donor-recipient pairs (DRP) with higher inhibitory KIR-KIRL interaction and missing KIRL (mKIR) scores, with HR=0.86 (P=0.01) & HR=0.84 (P=0.02) respectively. This effect was not observed with activating KIR-KIRL interactions. Chronic GVHD and TRM were not significantly affected by iKIR, mKIR or aKIR. Given the significant individual impact of iKIR and mKIR, the summed inhibitory-missing ligand (IM-KIR) score was next assessed, and when this score was 5 (as opposed to This large international study confirms that unrelated DRPs with greater magnitude of inhibitory KIR-KIRL interactions confer significant relapse protection after MUD HCT in standard-risk AML. This challenges the notion that KIR are irrelevant to donor selection. Future clinical trials evaluating donor selection for URD HCT should include this measure to evaluate its value prospectively in uniformly treated patient cohorts, with adequate GVHD and antiviral prophylaxis to mitigate TRM. Disclosures No relevant conflicts of interest to declare.

Immune reconstitution is critical to long term survivability in recipients of allogeneic hematopoietic cell transplantation (HCT), mitigating both relapse as well as infection risk. However, both graft versus host disease (GVHD) and post HCT immunosuppression used to prevent it impair immune recovery, particularly functional B cell reconstitution which may not happen for several months post-transplant. This is relevant for post-transplant vaccination which in some centers is delayed till immune cell recovery. In this retrospective, Virginia Commonwealth University institutional review board (IRB) approved study, T helper and B cell recovery for up to two years following HCT was evaluated in 212 patients transplanted between 2015 and 2019. There were 69 HLA matched related & 143 unrelated donor transplant recipients. Median age of the patients was 56 years (range 19-74); conditioning regimens utilized were reduced intensity (RIC) in ~62% of the patients and rabbit anti-thymocyte globulin was used in ~72% of the patients. Blood stem cells were given in 183 patients and bone marrow in 29. Only patients with hematological malignancies were included in this study. Landmark analysis was carried out, with patients who did not survive the first 6 months post-transplant excluded. Of these patients, 85% are surviving. Median CD3+/4+ (Th) cell counts were 153 at 6 months, 228 at 1-year, 296 at 2 years, and corresponding B cell counts were 70, 175, & 273. Plotting Th and B cell counts over time in each individual donor-recipient pair demonstrated close correspondence between Th and B cell recovery, with synchronous recovery observed in most patients, median R 0.76 (range: 0.01-0.99). The slope of the B/Th cell curves for each patient then were compared in a subset of patients, and demonstrated a significant difference between those patients who either did not develop GVHD or only had acute GVHD as opposed to those who developed both acute and chronic GVHD (1.3±1.4 B cells/Th cells and 1.1±1.2 vs. 0.5±1, P=0.02 and 0.06 respectively), suggesting poor B cell recovery in those with chronic GVHD. Different immune recovery kinetics were observed amongst patients (Figure 1); A) rapid B cell recovery, highest absolute B cell count between 30 and 180 days post-HCT, B) intermediate B cell recovery, days 180 and 455, C) delayed B cell recovery, days 455 and 725 days, and D) minimal to no B cell recovery. A higher relative risk for developing acute + chronic GVHD was seen in the intermediate B cell recovery group when compared to those with delayed recovery, RR = 2.38 (95% CI 1.08-5.25). Functional B cell studies were performed in a subset, by measuring IgG levels and anti-pneumococcal antibody titers. Correlation was observed between Th cell count and IgG levels over time in individual patients (median R = 0.57). Pneumococcal titers were also measured at approximately 6 months, 1- and 2-years post-transplant as patients were given a series of PCV13 & PSV23 vaccinations 6 months after HCT. When the antibody titers against unique pneumococcal serotypes were analyzed in individual patients, these varied within each individual, following a declining trend in levels for antibodies against different serotypes; this decline occurred on a logarithmic scale suggesting differential immunogenicity of the pneumococcal antigens, and also mathematically ordered, rather than random Th and B cell responses (Figure 2A). When the serotypes with the highest titers in most patients were correlated with Th and B cell counts measured simultaneously, no association was observed. Further, when fold increase in pneumococcal titers beyond 1-year post transplant were compared across different groups of patients based on their GVHD status, no significant difference was observed in their antibody responses (Figure 2B). In conclusion, our data suggest synchronous Th and B cell reconstitution post allogeneic HCT, both in numeric and functional terms, and thus strategies to help promote T cell recovery, such as IL-7 administration post-transplant, are necessary to encourage optimal immune reconstitution. Vaccine responses beyond 6 months, as in the institutional practice reported here, are independent of GVHD status and numeric immune cellular recovery. These findings are consistent with the notion that immune recovery is a dynamical, rather than a stochastic process. Disclosures No relevant conflicts of interest to declare.

When selecting a human leukocyte antigen (HLA) matched unrelated donor (URD) for hematopoietic cell transplantation (HCT) it is generally accepted that donor age, sex, ABO blood group and viral serologic status should be considered. However, the inter-relationship among these variables is not well established and a consensus on how strongly to consider each variable has not been reached. Selection of the optimal donor gets more complicated as new donor recipient pair (DRP) selection parameters, including killer immunoglobulin-like receptors (KIR) haplotypes are included. In this study we seek to develop a logic-based method to reduce the inconsistencies in donor selection in the HLA matched HCT. Retrospective review of eligible adults with known KIR genotyping receiving HLA-A, B, C & DRB1 allelically matched URD HCT for hematologic malignancy. Donor recipient pairs were selected based on donor age, sex match, CMV sero-status match, and ABO compatibility when possible; KIR genotype was not considered in DRP selection. KIR-KIR ligand interactions were calculated for each DR pair and interaction unit values were ascribed as previously described and each DRP IM KIR score (eq. 1) was calculated. IM KIR Score = |iKIR| + |mKIRL| [1] Weights of each donor risk variable (age, sex, CMV & ABO match) contribution were ascribed using Cox regression methods and summed up to determine donor risk parameter. Donor risk parameters and reciprocal-IM-KIR were finally combined into a donor risk index. Ninety-eight DRP with known HLA & KIR genotyping were studied. A higher IM-KIR score describes a DRP with increased iKIR-KIR ligand interactions and missing KIR ligand interactions; which was associated with a favorable survival after HCT, HR of 0.44 (95%CI: 0.26 to 0.73; P=0.002). Univariate analysis of overall survival for donor age, sex match, ABO compatibility and CMV status were all statistically insignificant (p>0.05). Donor risk parameter was predictive of mortality with a hazard ratio (HR) of 2.76 (95% CI: 1.22-6.18, p=0.014). Combining the two into a donor risk index was predictive of survival with a HR of 2.38 (1.44-3.92, p=0.001). ROC-AUC comparison of survival for IM-KIR score and donor risk parameter showed AUCs of 0.63 and 0.67 respectively. Further, the combined donor risk index shows improved sensitivity and specificity over the donor risk parameter with AUCs of 0.72 and 0.67 respectively. A novel IM-KIR score independently predicts survival in HLA matched DRP, as does a formalized donor risk parameter which includes non-HLA donor characteristics. Moreover, their addition enhanced the specificity and sensitivity of predicting survival in these patients. If validated in a larger exploration and validation cohort this method of donor selection may improve the donor selection process, decreasing variability in clinical outcomes and improve overall survival.

Killer Immunoglobulin Like Receptors (KIR) are expressed on natural killer (NK) and T cell surface. KIR interactions with KIR-ligands have been implicated in outcomes of hematopoietic stem cell transplantation, placental implantation, autoimmune disease and viral infections. While these KIR interactions are clearly important our understanding of what governs their expression is lacking. The KIR Locus is made up of a highly polymorphic and homologous set of genes located on Chromosome 19q13.4 within the leukocyte receptor complex. Unique to the KIR Gene Cluster, KIR haplotypes not only vary allelically, but they also differ in the number of KIR genes present in different individuals, ranging from 7 to 12 genes. KIR haplotypes have been divided into 2 broad groups; Haplotypes A & B, based on the number of activating and inhibitory KIR genes they possess; where haplotype A contains only one activating allele KIR2DS4 and haplotype B contains various combinations of activating alleles. Expression of KIR on the NK cell surface stochastic, with some KIR found more commonly then others. In this abstract we aim to explore the relationship of KIR gene expression and the organization of the KIR gene locus using available genomic and tissue expression data. KIR gene coordinates on chromosome 19 were collected using the UCSC Genome Browser GRCh38/hg38 gene assembly and the NCBI gene website gene assembly NC_000019.10. Initial KIR gene nucleotide position along chromosome 19 were obtained and converted to angular distance (A.D. in radians) from reference. This was done to account for the double helical nature of DNA molecules, using the following equation A.D. = 2px/10.4; where x is the initial KIR gene nucleotide coordinate. Haplotype A was utilized as an initial test case as gene expression data are available for the genes in this haplotype. GTEX Portal was used to collect mRNA expression for each of the haplotype A genes, KIR-2DL1, -2DL3, -2DL4, -2DP1, -2DS4, -3DL1, -3DL2, -3DL3 & -3DP1, including total (median), splenic and whole blood expression in Reads/Kilobase of transcript/million mapped reads (RPKM). Gene expression was determined via RNA-seq of 53 tissues from 570 donors. KIR haplotype A is located along chromosome 19 between nucleotide position 55,236,713 and 55,370,584 which corresponded with an A.D. of 33,354,476 to 33,435,314 radians. When the KIR gene expression was aligned with the coordinates of the corresponding gene on the KIR locus a distinct periodic pattern of variation in expression levels was observed across the KIR genes comprising Haplotype A (Figure 1). This was true for total KIR expression from across various organs, as well as in blood and splenic tissue. This is borne out by expression data on several Haplotype A KIR genes reported in the literature (Figure 1, yellow curve). These observations suggesting that KIR gene expression may be a periodic function of the gene coordinates on the chromosome are analogous to the periodicity observed in T cell receptor VDJ recombination (Meier et al, BBMT 2019 25(5);868). This observation supports the idea that the spiral structure of the helical DNA molecules coiled around the histone molecules and their arrangement on chromosomes may have a fundamental influence on the expression of different genes, perhaps in conjunction with known epigenetic influence of DNA methylation and histone acetylation. This may also point to a role for the non-coding DNA in regulation of gene expression. We posit that the helical DNA chromosome structure may have a fundamental role in determining gene expression, as exemplified by the KIR and T cell receptor gene loci. This knowledge may allow an improved understanding of variability in global gene expression. Disclosures No relevant conflicts of interest to declare.

Background When selecting a human leukocyte antigen (HLA) matched unrelated donor (URD) for hematopoietic cell transplantation (HCT) it is generally accepted that donor age, sex, ABO blood group and viral serologic status should be considered. However, the inter-relationship among these variables is not well established and a consensus on how strongly to consider each variable has not been reached. Selection of the optimal donor gets more complicated as new donor recipient pair (DRP) selection parameters, including killer immunoglobulin-like receptors (KIR) haplotypes are included. In this study we seek to develop a logic-based method to reduce the inconsistencies in donor selection in the HLA matched HCT. Methods VCU IRB approval was obtained for a retrospective review of eligible subjects who were adults with known KIR genotyping receiving HLA-A, B, C & DRB1 allelically matched URD HCT for hematologic malignancy between 2014 and 2017. Donor recipient pairs were selected based on donor age, sex match, CMV sero-status match, and ABO compatibility when possible; KIR genotype was not considered in DRP selection. KIR-KIR ligand interactions were calculated for each DR pair and interaction unit values were ascribed as follows; -1, when the donor possessed an inhibitory KIR (iKIR) and the recipient the corresponding HLA; +1, when the donor possessed iKIR and recipient lacked corresponding HLA (mKIR score, missing ligand). A novel inhibitory-missing KIR (IM-KIR) score was calculated for each HLA matched DRP by summing the interaction values as in equation 1. IM KIR Score = |iKIR| + |mKIRL| ………. [1] Univariate and multivariate analysis using Cox regression methods were utilized to evaluate donor parameters associated with overall survival. Weights of each donor risk variable (age, sex, CMV & ABO match) contribution were ascribed and summed up to determine donor risk parameter. Donor risk parameters and reciprocal-IM-KIR were finally combined into a donor risk index. Receiver operating characteristic curve- area under the curve (ROC-AUC) analysis was utilized to compare indices. Results Ninety-eight DRP with known HLA & KIR genotyping were studied. Median follow up at the time of analysis was 583 days. A higher IM-KIR score describes a DRP with increased iKIR-KIR ligand interactions and missing KIR ligand interactions; which was associated with a favorable survival after HCT, HR of 0.44 (95%CI: 0.26 to 0.73; P=0.002). Further analyses were performed using a reciprocal of this score. Univariate analysis of overall survival for donor age, sex match, ABO compatibility and CMV status were all statistically insignificant (p>0.05). However, the donor risk parameter was predictive of mortality with a hazard ratio (HR) of 2.76 (95% CI: 1.22-6.18, p=0.014). Covariate analysis of the donor risk parameter and reciprocal IM-KIR score were both predictive of survival independent of each other with HR 2.41 (1.05-5.54, p=0.038) and 2.35 (1.18-4.70, p=0.016) respectively. Combining the two into a donor risk index was predictive of survival with a HR of 2.38 (1.44-3.92, p=0.001). ROC-AUC comparison of survival for IM-KIR score and donor risk parameter showed statistically significant AUCs of 0.63 and 0.67 respectively. Further, the combined donor risk index shows improved sensitivity and specificity over the donor risk parameter with AUCs of 0.72 and 0.67 respectively. Conclusions A novel KIR-HLA interaction score, the IM-KIR score independently predicts survival in HLA matched DRP, as does a formalized donor risk parameter which includes non-HLA donor characteristics. Moreover, the addition of IM-KIR score to the donor risk parameter enhanced the specificity and sensitivity of predicting survival in these patients. If validated in a larger exploration and validation cohort this method of donor selection may improve the donor selection process, decreasing variability in clinical outcomes and improve overall survival. Disclosures No relevant conflicts of interest to declare.

Introduction Patients who receive HLA matched allogeneic hematopoietic cell transplant (HCT) from donors with killer immunoglobulin-like receptor (KIR) haplotype B have improved survival, decreased acute GVHD, and less CMV reactivation when compared with those transplanted with KIR haplotype A donors. However, the effect of NK cell (CD56+) reconstitution kinetics on clinical outcomes in patients with different KIR haplotypes is not well studied. Objectives Compare CD 56+ cell reconstitution kinetics in HCT patients with donor KIR Haplotypes A and B and its effect on clinical outcomes. Methods We assessed absolute NK and T cell counts at days +30, +60 and +100 in 10/10 allele level HLA matched unrelated HCT recipients with known donor KIR typing. KIR haplotype B was assigned when KIR2DL5, KIR2DS1, KIR2DS2, KIR2DS3, KIR2DS5 or KIR3DS1 were present in the donor, and haplotype A in their absence. We also evaluated potential impact of NK cell and T cell count recovery on key post transplant outcomes in these patients. Results The study population consisted of 60 adult HCT patients with a median age of 52 years; 55% had lymphoid and 45% had myeloid disease; 57% received a reduced intensity conditioning regimen; 82% underwent T cell depletion with ATG; 88% received GCSF mobilized PBSCT. Recipients of donor haplotype A had a median absolute CD56+ cell count of 210mL−1 (±156) on day (d) +30; 189 (±225) on d+60, and 160 (±120) on d+100; recipients of haplotype B had median absolute CD56 cell counts of 286 (±276) on d+30, 196 (±194) on d+60, and 165 (±124) on d+100 (P=N.S. for haplotype B vs. A). As a whole, median CD56+ cell counts peaked at d+30 post HCT, a phenomenon more pronounced in haplotype B (fig. 1), and then declined at d+60 and d+100. There was no correlation between CD56 and CD3 at d+60. Survival was superior in patients who had CD56+ cell count > median for the entire cohort (227 µL−1) on d+60 (p= .039) (fig. 2); ROC-AUC analysis confirmed the deleterious effect of low NK cell counts, with a higher mortality rate observed in those with CD56+ cell count of Conclusions The magnitude of NK cells reconstitution at d+60 may override the effect of KIR Haplotype on survival in patients with myeloid and lymphoid malignancies, as well as play an important role in controlling viral reactivation. Our data demonstrates that poor NK cell recovery does not necessarily imply delayed T cell reconstitution; suggesting that the adverse survival effect may be NK cell mediated. Ongoing work is examining relationship between NK- and T-cell reconstitution as well as KIR-KIR ligand interactions, and clinical outcomes.