Ipilimumab reshapes T cell memory subsets in melanoma patients with clinical response

Abstract

Purpose: Therapy targeting CTLA-4 immune checkpoint provides increased survival in patients with advanced melanoma. However, immunotherapy is frequently associated with delayed and heterogeneous clinical responses and it is important to identify prognostic immunological correlates of clinical endpoints.

Experimental design: 77 patients with stage III/IV melanoma were treated with ipilimumab alone every 3 weeks, during 9 weeks. Blood samples were collected at the baseline and before each dose for in depth immune monitoring.

Results: The median follow-up was 28 mo with a median survival of 7 mo. Survival and clinical benefit were significantly improved when absolute lymphocyte count at the baseline was above 1 × 10(9)/L. Notably, ipilimumab had a global effect on memory T cells, with an early increase of central and effector subsets in patients with disease control. By contrast, percentages of stem cell memory T cells (TSCM) gradually decreased despite stable absolute counts and sustained proliferation, suggesting a process of differentiation. Higher proportions of eomes(+) and Ki-67(+) T cells were observed, with enhanced skin homing potential and induction of cytotoxic markers.

Conclusion: These results suggest that CTLA-4 blockade is able to reshape the memory subset with the potential involvement of Eomes and memory subsets including TSCM.

Keywords: CTLA-4; TSCM; immunotherapy; ipilimumab; melanoma; memory T cells.

Figure 1.

Patients immunological status at the baseline. Percentages of CD4⁺ (A) and CD8⁺ (B) T cell subsets (CM for central memory, EM for effector memory, EMRA for terminally effector memory, GzmB for Granzyme B). Results from HD and patients are shown as open bars and black bars respectively. *for p < 0.05, ** for p < 0.01, *** for p < 0.001 and **** for p < 0.0001. (C) Kaplan–Meier survival curves from patients with ALC ≥ 1 × 10⁹/L (gray line, n = 43) or < 1 × 10⁹/L (black line, n = 26) at the baseline.

Figure 2.

Ipilimumab induces activated and memory T cells. The two slope model is visualized by the black line. CD4⁺ and CD8⁺ T cell subsets are presented in the left and the right panels respectively. (A) Percentage of HLA-DR⁺ T cells, absolute counts per mm³ of (B) CM, (C) EM and (D) EMRA. The same results are observed in terms of percentages of parental subsets (data not shown). *for p < 0.05, ** for p < 0.01, *** for p < 0.001 and **** for p < 0.0001.

Figure 3.

Pharmacodynamic changes during ipilimumab therapy. Expression of eomes on CD4⁺ and CD8⁺ T cells (A), T-bet (B) and CD122 (C) on. Cytotoxic markers expression (GzmB and TNF-a) on CD8⁺ T cells (D). Evolution of chemokine receptor expression in T cells (E). Note: T-bet and GzmB were evaluated on 20 patients as mentioned in material and method section. *for p < 0.05, ** for p < 0.01, *** for p < 0.001 and **** for p < 0.0001.

Figure 4.

CTLA-4 blockade and markers associated with clinical response. Patients were subdivided in two groups, DC (gray line and dots) and NR (black line and dots). Clinical benefit is associated with a more marked increase of memory subsets (A and B) and of eomes expressing CD8⁺ T cells (C). *for p < 0.05, ** for p < 0.01

Figure 5.

Ipilimumab induces a dynamic interplay between TSCM and classical memory T cells. Among memory subsets, only TSCM decrease in percentages (A) with constant absolute counts (B). The proliferative capacity of naïve, memory and TSCM subsets was assessed by Ki67 expression (C).