The majority of lung cancer patients progressing from conventional therapies are refractory to PD ‐L1/ PD ‐1 blockade monotherapy. Here, we show that baseline systemic CD 4 immunity is a differential factor for clinical responses. Patients with functional systemic CD 4 T cells included all objective responders and could be identified before the start of therapy by having a high proportion of memory CD 4 T cells. In these patients, CD 4 T cells possessed significant proliferative capacities, low co‐expression of PD ‐1/ LAG ‐3 and were responsive to PD ‐1 blockade ex vivo and in vivo . In contrast, patients with dysfunctional systemic CD 4 immunity did not respond even though they had lung cancer‐specific T cells. Although proficient in cytokine production, CD 4 T cells in these patients proliferated very poorly, strongly co‐upregulated PD ‐1/ LAG ‐3, and were largely refractory to PD ‐1 monoblockade. CD 8 immunity only recovered in patients with functional CD 4 immunity. T‐cell proliferative dysfunctionality could be reverted by PD ‐1/ LAG ‐3 co‐blockade. Patients with functional CD 4 immunity and PD ‐L1 tumor positivity exhibited response rates of 70%, highlighting the contribution of CD 4 immunity for efficacious PD ‐L1/ PD ‐1 blockade therapy.

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Hyperprogressive disease (HPD) is an adverse outcome of immunotherapy consisting of an acceleration of tumor growth associated with prompt clinical deterioration. The definitions based on radiological evaluation present important technical limitations. No biomarkers have been identified yet. In this study, 70 metastatic NSCLC patients treated with anti-PD-1/PD-L1 immunotherapy after progression to platinum-based therapy were prospectively studied. Samples from peripheral blood were obtained before the first (baseline) and second cycles of treatment. Peripheral blood mononuclear cells (PBMCs) were isolated and differentiation stages of CD4 lymphocytes quantified by flow cytometry and correlated with HPD as identified with radiological criteria. A strong expansion of highly differentiated CD28− CD4 T lymphocytes (CD4 THD) between the first and second cycle of therapy was observed in HPD patients. After normalizing, the proportion of posttreatment/pretreatment CD4 THD was significantly higher in HPD when compared with the rest of patients (median 1.525 vs. 0.990; p = 0.0007), and also when stratifying by HPD, non-HPD progressors, and responders (1.525, 1.000 and 0.9700 respectively; p = 0.0025). A cut-off value of 1.3 identified HPD with 82% specificity and 70% sensitivity. An increase of CD28− CD4 T lymphocytes ≥ 1.3 (CD4 THD burst) was significantly associated with HPD (p = 0.008). The tumor growth ratio (TGR) was significantly higher in patients with expansion of CD4 THD burst compared to the rest of patients (median 2.67 vs. 0.86, p = 0.0049), and also when considering only progressors (median 2.67 vs. 1.03, p = 0.0126). A strong expansion of CD28− CD4 lymphocytes in peripheral blood within the first cycle of therapy is an early differential feature of HPD in NSCLC treated with immune-checkpoint inhibitors. The monitoring of T cell dynamics allows the early detection of this adverse outcome in clinical practice and complements radiological evaluation.

Lymphocyte activation gene 3 (LAG-3) is a cell surface inhibitory receptor with multiple biological activities over T cell activation and effector functions. LAG-3 plays a regulatory role in immunity and emerged some time ago as an inhibitory immune checkpoint molecule comparable to PD-1 and CTLA-4 and a potential target for enhancing anti-cancer immune responses. LAG-3 is the third inhibitory receptor to be exploited in human anti-cancer immunotherapies, and it is considered a potential next-generation cancer immunotherapy target in human therapy, right next to PD-1 and CTLA-4. Unlike PD-1 and CTLA-4, the exact mechanisms of action of LAG-3 and its relationship with other immune checkpoint molecules remain poorly understood. This is partly caused by the presence of non-conventional signaling motifs in its intracellular domain that are different from other conventional immunoregulatory signaling motifs but with similar inhibitory activities. Here we summarize the current understanding of LAG-3 signaling and its role in LAG-3 functions, from its mechanisms of action to clinical applications.