Infectious Complications in Patients Treated with Idecabtagene Vicleucel for Relapsed and Refractory Multiple Myeloma

Introduction:

Chimeric antigen receptor (CAR) T-cell therapy is a novel adoptive immunotherapy utilizing autologous T cells expressing synthetic fusion proteins that target specific antitumor antigens. Over recent years, novel CAR T-cell constructs have shown efficacy for the treatment of hematologic malignancies. The B-cell maturation antigen (BCMA)-directed CAR T-cell product idecabtagene vicleucel (ide-cel) is the first approved CAR T-cell therapy for the treatment of multiple myeloma (MM). While ide-cel represents an important advance in MM treatment, it is critical to better characterize the risk of infectious diseases following this novel therapy.

Methods:

We investigated infectious complications in 27 (CRB-401, n/62; KarMMa, n/128) adult patients who received ide-cel for relapsed and refractory MM at two institutions. Patients were enrolled in an open label, multi-site Phase 1 or 2 clinical trial (NCT02658929; NCT03361748) evaluating the safety and efficacy of ide-cel. All participants received a 3-day cycle of lymphodepleting chemotherapy with fludarabine and cyclophosphamide 5 days prior to infusion and ide-cel was administered at target doses of 150×10 ⁶ to 450×10 ⁶ CAR-positive T cells. All patients but one received antiviral prophylaxis with val/acyclovir or famciclovir. Seventeen patients received pneumocystis prophylaxis with atovaquone or trimethoprim-sulfamethoxazole. Only 2 patients received antibacterial prophylaxis with levofloxacin and no patients received antifungal prophylaxis. Infections were retrospectively identified from day of cell infusion (day 0) up to day 100 after infusion. Infections were reported if patients experienced symptoms with a microbiologic or histopathologic diagnosis, or for symptomatic site-specific infections in conjunction with radiographic or exam findings and treatment with systemic antimicrobials. Infection severity was determined using the Blood and Marrow Transplant Clinical Trials Network criteria. Cytokine release syndrome (CRS) events were graded according to the Lee criteria. Patients were censored on date of disease relapse, the last day of the study period, or death.

Results:

Median age was 59 (range 41 - 79), 56% were males. Patients had received a median of 6 previous antimyeloma regimens (range 3 - 10); and 74% had undergone prior autologous hematopoietic cell transplantation. Following infusion of cells, 24 patients (89%) developed CRS with 54% of those receiving ≥ 1 dose of tocilizumab and 17% receiving ≥ 1 dose of corticosteroid. Only two patients (7%) developed CAR T cell associated neurotoxicity (ICANS) and one of those patients received treatment with corticosteroids. Eight patients experienced 19 infection-related events over the first 100 days after ide-cel infusion. To determine infection density, we evaluated 27 patients contributing 667 days at risk between d0 and d30 and 1777 days at risk between d0 and d100. Median time to first infection was 22 days (range 0 - 85). The estimated infection density was 1.8 infections per 100 patient days over the first 30 days, and decreased to 1.1 infections per 100 patient days from day 30 to d100. Among the infection events, bacterial infections were the most common (74%) with 6 bloodstream infections (32%) observed. Viral infections were less frequent (21% of events) and only one fungal infection (5% of events) was observed during the at-risk period. Four infections were of moderate severity; 10 were severe; and 5 were life-threatening. Eleven of the 27 patients (41%) had persistent neutropenia (absolute neutrophil count <1000) after day 30.

Conclusions:

Our study in this cohort of patients provides clarity on specific infectious complications in a unique population, and is of particular relevance given the recent FDA approval of ide-cel. Of note, these results represent a cross study single institution subgroup analysis that may not reflect the complete trial data. The overall incidence of infection was similar to what has previously been reported in patients receiving CD-19 directed CAR T-cell therapy, even with persistent neutropenia after one month documented in 41% of patients. Bacterial infections were the most common, and there were 5 life-threatening bacterial infections within the first 30 days after infusion. Notably, patients in this group experienced only 1 fungal infection, despite no patients receiving antifungal prophylaxis.

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