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Data are scarce regarding both the safety and immunogenicity of the BNT162b2 mRNA COVID-19 vaccine in patients undergoing immune cell therapy; thus, we prospectively evaluated these two domains in patients receiving this vaccine after allogeneic hematopoietic cell transplantation (HCT; n = 66) or after CD19-based chimeric antigen receptor T cell (CART) therapy (n = 14). Overall, the vaccine was well tolerated, with mild non-hematologic vaccine-reported adverse events in a minority of the patients. Twelve percent of the patients after the first dose and 10% of the patients after the second dose developed cytopenia, and there were three cases of graft-versus-host disease exacerbation after each dose. A single case of impending graft rejection was summarized as possibly related. Evaluation of immunogenicity showed that 57% of patients after CART infusion and 75% patients after allogeneic HCT had evidence of humoral and/or cellular response to the vaccine. The Cox regression model indicated that longer time from infusion of cells, female sex, and higher CD19+cells were associated with a positive humoral response, whereas a higher CD4+/CD8+ratio was correlated with a positive cellular response, as confirmed by the ELISpot test. We conclude that the BNT162b2 mRNA COVID-19 vaccine has impressive immunogenicity in patients after allogeneic HCT or CART. Adverse events were mostly mild and transient, but some significant hematologic events were observed; hence, patients should be closely monitored.

Patients with delayed B-cell reconstitution/B-cell aplasia after cellular therapy show decreased immunogenicity to the BNT162b2 mRNA COVID-19 vaccine. We prospectively evaluated both humoral and cellular immune response to a third vaccine dose in patients after allogeneic HCT (n = 10) or CD19-based chimeric antigen receptor T cells (CAR-T) therapy (n = 6) with low absolute B cell numbers and who failed to mount a humeral response after 2 vaccine doses. Humoral response was documented in 40% and 17% after allogeneic HCT and CAR-T therapy, respectively. None of the patients with complete B-cell aplasia developed anti-vaccine antibodies. Cellular response was documented in all patients after allogeneic HCT and in 83% of the patients after CAR-T. T-cell subclasses levels were not predictive for response, while a longer duration from infusion of cells was associated with a better cellular response. We conclude that cellular response develops with repeated vaccine doses even in patients with B-cell aplasia or delayed B-cell reconstitution, and these patients should therefore be vaccinated. These results should be considered in future studies analyzing immunogenicity in this population. Larger and longer follow-up studies are required to confirm whether cellular immunogenicity translates into vaccine efficacy.

Introduction - Data regarding efficacy and toxicity of different bridging strategies prior to CAR-T therapy are scanty. Tisagenlecleucel (Kymriah TM, Novartis) and axictagene ciloleucel (Yescarta TM, Kite/Gilead) were commercially approved for relapsed/refractory (R/R) DLBCL since 2019. We analyzed real-life data of CAR-T therapy among all consecutive patients who were treated in 4 different CAR-T centers in Israel.

Ram: Gilead: Honoraria; Novartis: Honoraria. Yehudai-Ofir: Novartis: Membership on an entity's Board of Directors or advisory committees; Gilead Sciences: Membership on an entity's Board of Directors or advisory committees. Avivi: Novartis: Speakers Bureau; Kite, a Gilead Company: Speakers Bureau. Zuckerman: Cellect Biotechnology: Honoraria; Gilead Sciences: Honoraria, Speakers Bureau; Novartis: Honoraria; Janssen: Honoraria; BioSight Ltd: Honoraria; Orgenesis Inc.: Honoraria; AbbVie: Honoraria. Yeshurun: Astellas: Consultancy; Janssen: Consultancy. Gurion: Medison; Gilead Sciences; Takeda Pharmaceuticals: Consultancy; JC Health CARE; Roche: Honoraria. Levi: AbbVie: Consultancy, Research Funding.