Clinical Factors Associated with Improved Survival Following Allogeneic HSCT after CD19 CAR Therapy in Adult Patients with Relapsed B-ALL

Introduction: Autologous chimeric antigen receptor (CAR) T cell therapy has shown to be effective in CD19+ relapsed or refractory (R/R) B-ALL patients (pts). However, relapses are common and the role of post-CAR allogeneic hematopoietic stem cell transplant (alloHSCT) remains unclear, particularly in adults with relapsed B-ALL. We previously reported that there was no survival benefit with post-CAR alloHSCT in overall adult ALL population (Park J et al. NEJM 2018), but it is unclear whether there is a subset of pts who may benefit the most from post-CAR alloHSCT. Therefore, we sought to identify clinical features that are associated with a better long-term survival in adult B-ALL pts treated with CD19 CAR T cells followed by alloHSCT.

Methods: We performed a retrospective chart review of adult pts with R/R ALL treated with 19-28z CAR T therapy at MSKCC (NCT01044069), with a particular focus on pts who achieved minimal residual disease (MRD) negative CR to the CAR therapy and subsequently proceeded to alloHSCT. Clinical data was updated with the data cutoff date of July 15, 2019. We examined the association between overall survival and the following clinical factors: impact of age, prior HSCT status, presence of Philadelphia chromosome (Ph), disease status at the time of CAR therapy (MRD vs. morphologic), severity of cytokine release syndrome (CRS) and neurotoxicity (NTX) experienced during CAR therapy. Survival was calculated from the time of CAR T cell infusion. Continuous variables were analyzed univariately using cox PH models. Categorical variables were analyzed using Kaplan Meier methodology and log rank tests.

Results: Of the 53 pts who received 1928z CAR T cells, 16 pts proceeded to alloHSCT after achieving MRD negative CR to the CAR therapy. The median age of these pts was 38 (range, 23-66), and baseline disease and pt characteristics as well as response and toxicity to CAR T therapy are listed in Table 1. Of the 16 pts, 6 pts remain alive in remission; 4 pts died of relapse (median time to relapse: 104.5 days, 57-194), and 6 pts died of transplant-related mortality (TRM) in remission (n=4, infection; n=1, pulmonary VOD; n=1, respiratory failure of unclear etiology). Detailed disease and treatment characteristics by the outcome categories are listed in Table 2. For those pts who are alive in remission, the median survival is 47.5 months (range, 39.7-92.4). Among the examined clinical variables, we found younger age and no severe NTX (i.e. grade 0-2) after CAR therapy to be significantly associated with improved overall survival (p=0.014 and 0.05, respectively) but prior lines of therapy, time to HSCT, prior HSCT, Ph chromosome, disease status at the time of T cell therapy and severity of CRS did not impact the survival after alloHSCT.

Conclusions: In this retrospective analysis, we found that younger age and no severe NTX to CD19 CAR therapy were associated with improved overall survival following alloHSCT. Number of relapses following alloHSCT (4 of 16 pts) appears to be lower compared to the previously reported number of relapse in the adult ALL cohort without alloHSCT (17 of 26 pts). However, the occurrence of TRM due to infection is high, likely a reflection of heavily pretreated pt population and possibly further immunosuppression from CAR + alloHSCT. The link between severe NTX and worse survival is unclear but could be related to prolonged corticosteroid use and high disease burden. While no definitive conclusion can be drawn due to a small sample size, our data suggests a certain subset of adult pts with R/R B-ALL may benefit more from alloHSCT as a consolidation therapy following CD19 CAR T cells, and acute and late infectious complications following alloHSCT should be carefully monitored. These findings should be validated prospectively and compared between different CAR constructs.

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