Baseline intratumoral CD4⁺ T-cell abundance and frequency correlates with durable clinical response to acalabrutinib, venetoclax, and obinutuzumab (AVO) treatment in Mantle Cell Lymphoma Free

Mantle cell lymphoma (MCL) is a heterogeneous and currently incurable B-cell malignancy. As the tumor immune microenvironment (TIME) critically influences response to targeted and immune-based therapies, it has emerged as a key area of investigation in MCL. However, most established MCL biomarkers are tumor-intrinsic (e.g., TP53 mutation, Ki-67), and there remains an unmet need for validated immune biomarkers to guide patient stratification and optimize treatment selection. We sought to interrogate TIME-associated predictive biomarkers within the context of an ongoing phase 1/2 clinical trial (NCT04855695) investigating the chemotherapy-free combination of acalabrutinib, venetoclax, and obinutuzumab (AVO) in patients with relapsed/refractory MCL (cohort A) and treatment-naïve TP53 aberrant or transplant ineligible MCL (Cohort B).

Durable responders were defined as patients who maintained clinical remission for ≥24 months without disease progression, while non-durable responders progressed or relapsed within 24 months of treatment initiation. Two patients were not evaluable for response categorization: one discontinued treatment early due to adverse events, and the other died from an unrelated cause shortly after enrollment, before disease assessment could be performed. Baseline biopsy specimens (lymph node, bone marrow, skin, cervical, or soft tissue) with confirmed MCL involvement were collected from patients enrolled in the AVO clinical trial. Multiplex immunofluorescence (mIF) was performed to identify tumor cells, T cell subsets, dendritic cells, and macrophages. Among 44 enrolled patients, 26 quality-controlled baseline specimens from 23 evaluable patients (11 from Cohort A and 10 from Cohort B; a median follow-up: 20.5 months) were included in the quantitative spatial analysis. For Cohort A (median follow-up: 26.4 months), all durable responders had ≥24 months of follow-up. In Cohort B (median follow-up: 18.9 months), only two responders reached the 24-month threshold, while others had follow-up ranging from 14.4 to 20.5 months (median: 18.7 months). The remaining Cohort B patients with <24 months of follow-up who had not progressed were provisionally classified as durable responders for exploratory analysis, acknowledging that their status is subject to change with longer follow-up.

Quantitative spatial profiling revealed that in the Cohort A, durable responders (n = 8; mean CD4⁺ T-cell density: 1952 cells/mm²) exhibited significantly greater intratumoral CD4⁺ T-cell density within baseline TIME compared to non-durable responders (n = 3; mean: 458.7 cells/mm²; p = 0.0370). In Cohort B, durable responders (n = 10; mean: 1820 cells/mm²) showed a nominal increase in CD4⁺ T-cell density compared to non-durable responders (n = 2; mean: 434.6 cells/mm²; p = 0.1854), though this difference did not reach statistical significance. These associations remained consistent when assessed by both absolute cell density and proportion of total cells and were independent of overall non-tumor cell content. In contrast, CD8⁺ T-cell, dendritic cell, macrophage, and tumor cell densities or proportions showed no association with response status. A provisional CD4⁺ T-cell proportion threshold of 6.11% (median across all patients) was used to stratify patients. Kaplan–Meier analysis revealed that patients with CD4⁺ proportions >6.11% had significantly improved progression-free survival (PFS) in Cohort A (p = 0.0315). Similar trends were observed in Cohort B (p = 0.2253) and the combined A and B cohorts (p = 0.0091), as assessed by the log-rank (Mantel–Cox) test.

A higher proportion of baseline intratumoral CD4⁺ T cells was associated with durable clinical responses to AVO therapy in MCL. CD4⁺ T cell abundance and frequency- but not CD8⁺ T cell, dendritic cell, macrophage or tumor cell levels- was associated with clinical benefit. Although the AVO regimen does not directly target T cells, these findings are hypothesis-generating. Continued evaluation of expanded cohorts, post-treatment biopsy specimens, and spatial neighborhood interactions aims to further elucidate immune mechanisms of response.