Tohumeken, S.; Mostafa, A.; Binjawadagi, R.; Mai, M.; Paucarmayta, A.; Merlano, A. M. M.; Youn, C.; Chang, E.; Shah, P.; Chow, H.; Moulton, W.; Luo, X.; Tam, K. B.; Flynn, M.; Wetzel, L.; Walseng, E.; Galery, E. H.; Boland, J.; Huntley, A.; Kiefer, C.; Zhang, J.; Mendoza-Topaz, C.; Cayatte, C.; Bergamaschi, C.; omar, B.; Sapra, P.; Cobbold, M.; sanseviero, E.; Gabrilovich, D.

Background. Antibody drug conjugates (ADCs) represent a transformative class of cancer therapeutics, yet the mechanisms underlying their synergy with immunotherapy remain poorly understood. We investigated the mechanistic basis of ADC combinations with T cell engagers (TCEs) and checkpoint inhibitors (CPI). Methods ADC/TCE and ADC/CPI combinations were evaluated in vitro using co culture cytotoxicity assays and synergy analyses, and in vivo in humanized mouse tumor models. Mechanistic studies employed TNF and cytokine blocking antibodies, receptor knockout cell lines, autophagy inhibitors, and siRNA silencing. Results ADC/TCE combinations produced synergistic antitumor activity independent of target antigen and payload, persisting despite ADC induced T cell loss. ADC treatment induced autophagy, upregulating TNF receptors (TNFR1/2) and mannose 6 phosphate receptor (M6PR) on tumor cell surfaces. In ADC/TCE combinations, TCE derived TNF; acting on ADC upregulated TNFRs was the primary mediator of enhanced cytotoxicity, confirmed in vivo by TNF blockade. In contrast, combinations with CPI expanded antigen specific T cells operated through a TNF independent, M6PR dependent pathway involving enhanced granzyme B uptake. Conclusions ADC induced autophagy is a unifying, target- and payload-agnostic mechanism sensitizing tumor cells to T cell mediated killing. TCEs exploit a TNF/TNFR axis, whereas antigen specific T cells leverage granzyme B/M6PR uptake. This mechanistic framework enables rational selection and design of ADC immunotherapy combination strategies.