Table 2.

Overview of coinhibitory and costimulatory markers assessed in various primary tumors. Markers were either assessed as single positive or double positive.

Primary tumor	Coinhibitory markers	Costimulatory marker	Main conclusions
Melanoma	PD1, CTLA4, LAG3, TIGIT, TIM3	2B4	• Continuous antigen stimulation decreases antitumor activity (101, 102)
			• Long-term remission in murine models after αLAG3 + αPDL1 (112, 113)
Lung cancer	PD1, CTLA4, LAG3, BTLA, CD69, TIM3	2B4	• Patients with a high CD4 PD-1+ frequency had decreased overall and progression-free survival, independent of clinical characteristics (145)
GBM	PD1, TIM3, LAG3, CTLA4		Majority of PD-1+ CD4 T cells were IL7Rα negative (104) Increased proliferation upon αPD1 observed only in the presence of PD1- CD4 T cells (95) PD1hi Tregs exhibit decreased suppressive functions and increased IFNγ production (114) Clonal expansion was observed among tumor-infiltrating CD4 T cells (8)
Breast	PD1, TIM3		αPD-1 treatment increased TCR signaling (97), proliferation (146), cytokine production (98) Overexpression of MHC-II on tumor cells reduces exhaustion in CD4 T cells and increases tumor control (18)
Head and neck	TIGIT, LAG3, TIM3, PD1, CD69		• αTIGIT delayed tumor progression, although direct effect on CD4 T cells not assessed (103)
Gastrointestinal	PD1, CTLA4, TIM3, LAG3	ICOS	Checkpoint inhibitors decreased suppressive ability of Tregs (147) and partially restored effector functions (84, 94) TIM3+ cells expressed increased cycle-dependent kinase inhibitors, preventing cell-cycle entry. αTIM3 restored cell proliferation (100)
AML	PD1, CD57, CD69, CTLA4, TIM3, LAG3	ICOS	• αCD86 and ICOS-ligand prevented the emergence of exhausted CD4 T cells (148)
CLL	PD1, TIM3, TIGIT	2B4, CD226	• αTIGIT impaired IFNγ and IL10 production in the presence of tumor cells the TIGIT ligand (CD155; ref. 111)
Multiple myeloma	PD1, TIM3, CTLA4	CD40L	• Gradual decrease in CD40L expression with more advanced disease (149)