TLR9 Agonists Potentiate Adoptive T Cell Therapy in Cancer Through a B Cell–CD2 Costimulatory Axis

Potentiation of adoptive T-cell therapy by Toll-like receptor 9 (TLR9) agonists is mediated through a B cell–CD2 costimulatory axis, according to a study in Cancer Research from Emory University's Winship Cancer Institute with collaborators at the University of Pennsylvania. Class B CpG activated B cells in a manner that improved CD8-positive T-cell differentiation, metabolism, cytotoxicity, and tumor control. Because the interaction occurs during expansion, enhancing CD2 signaling during TIL or CAR T-cell manufacturing may help overcome resistance in solid tumors without systemic TLR agonist administration.

Adoptive T-cell therapy can produce durable responses, but solid tumors often resist treatment through antigen heterogeneity, stromal exclusion, metabolic stress, and inhibitory signaling. Earlier work by this group established that brief exposure to class B CpG during ex vivo expansion improved T-cell efficacy and required interactions with B cells, although the responsible mechanism was unidentified. Multiple TLR agonists and CpG subclasses were compared in murine melanoma models, human peripheral blood cells, patient tumors, and mesothelin-targeted CAR T cells, and candidate costimulatory molecules were blocked individually.

Among the agonists tested, only class B CpG consistently programmed CD8-positive T cells for durable antitumor activity. Blocking CD2 reduced CD25 and ICOS expression, impaired glycolytic and fatty-acid metabolic capacity, increased mitochondrial stress, and eliminated tumor regression in both B16F10 and B16KVP melanoma models. Blocking CD28, CD80, CD86, ICOS, or CD40L did not reproduce this loss of efficacy. Direct CD2 stimulation increased tumor killing and improved human mesothelin CAR T-cell potency, and murine CARs incorporating a CD2 signaling domain outperformed 4-1BB-based constructs and matched CD28-based constructs. Human TLR9-activated B cells promoted TEMRA differentiation and increased granzyme B and perforin production. Across melanoma, breast cancer, and non-small cell lung cancer datasets, higher CD2 expression was associated with immunotherapy response and better survival. The B cell–CD2 axis therefore represents a targetable mechanism for improving adoptive cell therapy in solid tumors.

Reference:

Ruffin AT, Toliopoulos V, Smith AS, et al. TLR9 Agonists Potentiate Adoptive T Cell Therapy in Cancer through a B Cell-CD2 Costimulatory Axis. Cancer Res. Published online July 6, 2026. https://doi.org/10.1158/0008-5472.CAN-26-0202