Overcoming T cell dysfunction in acidic pH to enhance adoptive T cell transfer immunotherapy

Abstract

The high metabolic activity and insufficient perfusion of tumors leads to the acidification of the tumor microenvironment (TME) that may inhibit the antitumor T cell activity. We found that pharmacological inhibition of the acid loader chloride/bicarbonate anion exchanger 2 (Ae2), with 4,4'-diisothiocyanatostilbene-2,2'-disulfonicacid (DIDS) enhancedCD4⁺ andCD8⁺ T cell function upon TCR activation <i>in vitro</i>, especially under low pH conditions. <i>In vivo</i>, DIDS administration delayed B16OVA tumor growth in immunocompetent mice as monotherapy or when combined with adoptive T cell transfer of OVA-specificT cells. Notably, genetic Ae2 silencing in OVA-specificT cells improvedCD4⁺/CD8⁺ T cell function <i>in vitro</i> as well as their antitumor activity <i>in vivo</i>. Similarly, genetic modification of OVA-specificT cells to overexpress Hvcn1, a selectiveH⁺ outward current mediator that prevents cell acidification, significantly improved T cell function <i>in vitro</i>, even at low pH conditions. The adoptive transfer of OVA-specificT cells overexpressing Hvcn1 exerted a better antitumor activity in B16OVA tumor-bearingmice. Hvcn1 overexpression also improved the antitumor activity of CAR T cells specific for Glypican 3 (GPC3) in mice bearing PM299L-GPC3tumors. Our results suggest that preventing intracellular acidification by regulating the expression of acidifier ion channels such as Ae2 or alkalinizer channels like Hvcn1 in tumor-specificlymphocytes enhances their antitumor response by making them more resistant to the acidic TME.