Viral Reactivation and Immune Reconstitution after CAR-T Cell Treatment in Patients with Hematologic Malignancies

Background Chimeric antigen receptor (CAR)-T cell therapy is a promising immunotherapy for various hematologic malignancies. Whereas acute toxicities, such as cytokine release syndrome (CRS) and neurotoxicity, have been well studied, other adverse effects, such as immune deficiency, have not been well characterized yet. For example, data on reconstitution of lymphocyte subpopulations after CAR-T cell therapy and associated short and long-term risks of infectious complications is limited. The aim of our study was to analyze dynamics of lymphocyte reconstitution and its potential impact on infections after CAR-T cell therapy.

Patients and Methods We analyzed patients who underwent CAR-T cell treatment from 2019 to 2022 in our center. All CAR-T products and indications were eligible. All patients received lymphodepletion with fludarabine and cyclophosphamide as per protocol. Similar supportive care was used for all patients as per institutional guidelines, i.e EBV, CMV, HSV, HHV6/8 levels were investigated by PCR, and immunophenotypes by flow cytometry 1x/week until discharge, then 2x/week until day 30 and then 1x/2weeks until day 100. All patients received prophylaxis with acyclovir 400mg/3x/d for 6 months or until reconstitution. Recovery was defined as at least lower bound of lymphocyte reference counts.

Results A total of 63 patients were included: diffuse large B-cell lymphoma (n=54), mantle cell lymphoma (n=3), multiple myeloma (n=2), follicular lymphoma (n=1), acute lymphoblastic leukemia (n=1), and Richter transformation (n=1). Most CAR-Ts were autologous (n=59), and 4 were allogeneic (1 compassionate use, 3 on trial). 10 patients received autologous hematopoietic stem cell (HSC) boost for persistent neutropenia. Median age of all patients was 62 years (range, 23-84 years) and 64% (n=40) patients were male.

In terms of safety, 82% developed CRS - 29% grade 1, 46% grade 2 and 8% grade 3. Neurotoxicity was observed in 46%, grade 1 in 22%, grade 2 in 16%, grade 3 in 5% and grade 4 in 3%. In terms of efficacy, overall response rate was 57%, of which 30% were complete responses.

During overall follow-up, CMV reactivation occurred in 13 patients (21%), EBV and HSV reactivation each in 1 patient (2%). Median time to CMV reactivation was 17 days (range, 7-172 days). All events were transient, and none of the patients required specific antiviral treatment. Reactivation was associated with year of CAR-T infusion - most reactivated patients (n=10) were treated in 2019-2020.

At days 30 and 100, recovery was seen in 14% and 21% for T lymphocytes, 0% and 3% for B lymphocytes, 60% and 65% for NK cells, 17% and 24% for CD4+ cells, 52% respectively for CD8+ cells, and 2% and 0% for Treg cells. There was a significant interaction between patients who received an HSC boost and those who did not (P=0.02). At day 100, median number of T lymphocytes was 327/µl, T-helper cells 145/µl, cytotoxic T cells 168/µl, B lymphocytes 0/µl, NK cells 142 /µl, naïve CD4+ 11/µl, memory CD4+ was 106/µl, naïve CD8+ 75/µl, memory CD8+ 95/µl, gamma-delta T cells 6/µl, and Tregs 5/µl.

CMV reactivation was associated with slower immune reconstitution in terms of T lymphocytes (P=0.05), activated T lymphocytes (P=0.02), cytotoxic T cells (P=0.02), naïve and memory B cells (P=0.03 and 0.02), and gamma-delta T cells (P=0.05). Regarding response, faster recovery of NK cells was associated with response (P=0.04). CMV reactivation was associated with overall occurrence of ICANS (P=0.05) but not with ICANS grades nor with CRS.

Median follow-up of included patients was 10 months (95% confidence interval [CI], 7-12 months). Median overall survival was 19 months (95% CI, 11-28 months) and 1-year survival was 65% (95% CI, 51-79%). 1-year overall survival was 90% for patients with complete response, 67% for partial response, and 42% for <PR (P=0.02). 1-year progression-free survival was 55% (95% CI, 50-70%) and was 67% for patients with recovered NK cells (65-550) versus 40% for those without recovery (P=0.05). 6 events of non-relapse mortality occurred, of which 5 were infection-related (3 bacterial, 2 were SARS-CoV-2 positive), while 1 was severe macrophage-activation-syndrome.

Conclusion Viral reactivation after CAR-T cell therapy is uncommon and associated with immune reconstitution dynamics. Recovery of NK cells may be associated with response and thus, outcomes.

Kroeger:Novartis: Honoraria; Kite/Gilead: Honoraria. Ayuk:Novartis: Honoraria; Gilead: Honoraria; Janssen: Honoraria; Mallinckrodt/Therakos: Honoraria, Research Funding; Miltenyi Biomedicine: Honoraria; Takeda: Honoraria; Medac: Honoraria; Celgene/BMS: Honoraria.