B-Cell Lymphomas Secrete Novel Inhibitory Molecules That Disrupt HLA Class II-Mediated CD4+ T-Cell Recognition.

B-cell lymphomas, including Burkitt lymphoma (BL), diffuse large B-cell lymphoma (DLBCL), and follicular lymphoma (FL), evade CD4+ T-cell immunity through novel HLA class II-associated immunosuppressive mechanisms. Despite expressing surface HLA-DR, these tumors fail to activate antigen-specific CD4+ T cells, independent of co-stimulation or PD-L1 checkpoint inhibition. We identified lymphoma-secreted factors that broadly disrupt HLA class II-mediated antigen presentation in both malignant B cells and dendritic cells (DCs), silencing T-cell responses. This inhibition is allele-independent (affecting DR1, DR4, DR7) but spares HLA class I-mediated CD8+ T-cell recognition, indicating a targeted immune evasion strategy. Biochemical and mass spectrometry (MALDI-MS) analyses revealed unique low-molecular-weight peptides (693-790 Da) in BL cells, absent in normal B cells, which may mediate this suppression. Functional fractionation confirmed bioactive inhibitory fractions in lymphoma lysates, further implicating tumor-intrinsic molecules in immune escape. These findings highlight a previously unrecognized axis of B-cell lymphoma immune evasion, where secreted factors disable HLA class II function across antigen-presenting cells. Therapeutically, neutralizing these immunosuppressive molecules could restore CD4+ T-cell surveillance and enhance immunotherapies in B-cell malignancies. This work underscores the importance of HLA class II dysfunction in lymphoma progression and identifies candidate targets for reversing immune suppression.