Humoral and cellular responses to tisagenlecleucel

Chimeric antigen receptor (CAR) T-cell therapy has elicited high-response rates in patients with relapsed or refractory (R/R) B-cell malignancies such as diffuse large B-cell lymphoma (DLBCL) and B-cell precursor acute lymphoblastic leukemia (B-ALL). However, some concerns have been raised that the efficacy and safety of the CAR T-cell therapies may be impacted by the humoral and cellular immune response. This is of particular concern for CAR T-cell products with murine components such as tisagenlecleucel (tisa-cel). Specifically of interest are preexisting or posttreatment antibodies that may play a part in the immune response to CAR T-cells.

In a study by Karen Thudium Mueller and colleagues, the incidence and prevalence of immunogenicity against tisa-cel, an anti-CD19 CAR T-cell therapy, was examined in patients with R/R B-ALL and DLBCL.¹

Study design

Results from three clinical trials were incorporated in this study and in total, 258 patients were included. The effects of humoral and cellular immune responses to tisa-cel on cellular kinetics, clinical response, and safety were evaluated.

Efficacy endpoints included:

• Clinical response on Day 28 (complete remission [CR] + CR with incomplete hematologic recovery [CRi]) in patients with R/R B-ALL
• Best overall response (OR) within 3 months of tisa-cel infusion in patients with R/R B-ALL
• OR at Month 3 (CR + partial response [PR]) in patients with R/R DLBCL
• Duration of response (DOR)
• Progression-free survival (PFS)
• Overall survival (OS)

Safety endpoints included cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS).

For young adult and pediatric patients with R/R B-ALL (n = 143), the results included were from the:

• ELIANA phase II trial (NCT02435849)
• ENSIGN phase II trial (NCT02228096)

For adult patients with R/R DLBCL (n = 115), the JULIET phase II trial (NCT02445248) was included in the study.

Flow cytometric analysis was used to measure humoral immunogenicity. Samples were taken following lymphodepletion but before tisa-cel treatment, to act as a baseline.

Results

Humoral immunogenicity

In patients with R/R B-ALL, 81% harbored anti-mCAR19 antibodies, and in patients with R/R DLBCL, 94% were positive for anti-mCAR19 antibodies. Samples from healthy volunteers showed that 90% had pre-existing anti-mCD19 antibodies during method validation. Patients who had previously received murine or humanized monoclonal antibody treatment were as follows:

• 10% of patients with B-ALL (rituximab, n = 7; inotuzumab, n = 4; moxetumomab, n = 2; and alemtuzumab, n=1)
• 98% patients with DLBCL received rituximab before tisa-cel, ranging from >1 year prior to tisa-cel infusion (15%) to within 1 month of infusion (14%)

Cellular immunogenicity

Of the 143 patients with R/R B-ALL, 142 (99%) had T-cell responses < 1% to anti-mCAR19 peptides, and 107 of the 115 patients (93%) with R/R DLBCL had T-cell responses <1%. T-cell responses from B-ALL patients who were in the 90th percentile in terms of their T-cell responses were compared to the responses from the entire cohort to establish the impact of T-cell responses on cellular kinetics and clinical outcomes. In the B-ALL group, 14 patients were in the 90th percentile for T-cell responses but no noticeable differences were recorded between these patients and the wider group with respect to the following categories:

• Response categories
• CRS grade
• Maximum posttreatment transgene levels
• Persistence
• DOR

Cellular kinetics

There was no significant relationship between the maximum concentration after tisa-cel treatment and presence of preexisting anti-mCAR19 antibodies in either patients with R/R B-ALL or R/R DLBCL. Preexisting humoral responses did not affect transgene exposure (Days 0−28) in either group.

Regarding posttreatment levels of anti-mCAR19 antibodies:

• 42% of patients with R/R B-ALL had increased anti-mCAR19 antibodies compared to baseline
• 9% of patients with R/R DLBCL had increased anti-mCAR19 antibodies compared to baseline

In patients with R/R B-ALL, this increase in anti-CAR19 antibody levels did not affect tisa-cel expansion or persistence. There was insufficient data to assess this for the patients with R/R DLBCL.

Impact on efficacy outcomes

No effect was seen on the Day 28 response in patients with B-ALL regarding the presence of either preexisting or posttreatment antibodies. The same was true for patients with DLBCL at Month 3 response.

For patients with R/R B-ALL in the 90th percentile of mean fluorescence intensity (MFI) for anti-mCAR19 antibodies, the overall response rate (ORR) at Day 28 was 85% compared with 77% for the remainder of the population, and the best ORRs were 77% vs 74%, respectively. OS and DOR were unaffected by preexisting/posttreatment anti-mCAR19 antibodies in this group of patients with R/R B-ALL.

Impact on safety outcomes

Preexisting or posttreatment anti-mCAR19 antibodies did not impact safety (CRS or neurological events) in either group of patients. The impact on levels of infection in these patients was also examined but no association was found between anti-mCAR19 antibody levels and infection within the 8 weeks following infusion of tisa-cel.

Cellular immunogenicity and B-cell aplasia

Analysis showed that there was no relationship between level of anti-mCAR19 antibodies and duration of B-cell aplasia.

CD4+ and CD8+ T-cell responses to anti-mCAR19 antibodies were measured, and net responses were found to be <1% in patients with R/R B-ALL.

Tisa-cel expansion and persistence was not affected by CD4+ or CD8+ T-cell responses, and patient outcomes were not affected by the responses of these two groups of T-cells.

Conclusion

From the results of this study, no clinically meaningful effect was seen on patient response, safety outcomes or expansion and persistence of tisa-cel from preexisting/posttreatment anti-mCAR19 antibodies. In addition, it was common for healthy volunteers to have low levels of preexisting anti-mCAR19 antibodies. T-cell responses to anti-mCAR19 antibodies had no demonstrable impact on patient outcomes and cellular expansion in patients with R/R DLBCL or R/R B-ALL. Data on CAR-T immunogenicity are currently limited; however, a further study is needed to inform guidance for immunogenicity testing across CAR T-cell therapy.