T-cell large granular lymphocytic leukemia evolution post-transplant: The Cleveland Clinic experience

e19072 Background: T-cell large granular lymphocytic leukemia (LGLL) has been reported after solid organ transplantation (SOT) and hematopoietic stem cell transplantation (HSCT); yet its underlying pathophysiological evolution has been poorly explained. Methods: We retrospectively screened a cohort of 243 LGLL patients at Cleveland Clinic for disease development post-transplantation and postulated several possible responsible pathophysiological mechanisms. Results: Five percent (n = 12) of the patients had a history of transplant. Of these, 67% (n = 8) had SOT (kidney, liver or heart) while 33% (n = 4) had HSCT. Twenty-five percent were females while 75% were males. The median age was 56 years (range: 15-65). The median time from transplant to diagnosis was 7 years. Conventional cytogenetic showed normal karyotype in 89% of the patients. TCR gene re-arrangement by PCR was detected in all tested individuals. Targeted deep sequencing identified somatic STAT3 mutations in 17% (n = 2) of the cases. Fifty percent (n = 6) had EBV DNA, IgM and/or IgG post-transplant. Forty-two percent (n = 5) had CMV DNA, IgM and/or IgG; of which 80% (n = 4) were post-transplant and 20% (n = 1) pre-transplant. The median survival from disease diagnosis was 64.3 months (8.37-232.9). Indeed, T-LGL clonal expansion resulted from long-term stimulation by viral antigens including EBV and CMV causing continuous cytotoxic T cell immune response or by “oncomodulation” as explained in 83% of patients. The latter theory suggests that CMV infects tumor cells and modulates their malignant properties, without direct transformation. Immunosuppression in setting of pre-transplant exposure to CMV, caused reactivation of the latent oncogenic viral genome as seen in 8% of patients. In 17% of cases that were seronegative for viral genome, graft allo-antigenic stimulation has triggered long-term recipient LGLL expansion from antigenic mismatch. Somatic STAT3 mutations, which are highly expressed in leukemic LGL, has led to aberrant signaling and transformation (17%). Conclusions: Our study highlights the complex nature of LGLL evolution post SOT and HSCT and points out confounding mechanisms. Certainly, investigating pre- vs. post-transplantation baseline, clinical and molecular characteristics is warranted to deeply understand this phenomenon.