In a groundbreaking study published in Nature in 2026, researchers have unveiled compelling evidence on the intricate immune landscape underlying the efficacy of combined intratumoural anti-CTLA4 and intravenous anti-PD1 therapy in cancer patients. This innovative therapeutic approach appears to engage pre-existing adaptive immune responses, particularly those mediated by major histocompatibility complex (MHC) class I and II molecules, thereby delineating pathways associated with durable clinical benefit (DCB). The study deploys sophisticated multi-dimensional analyses including transcriptomic deconvolution, immunohistochemistry (IHC), and flow cytometry to dissect the tumor microenvironment and immunologic determinants of therapy responsiveness.
At baseline, tumors from patients who subsequently exhibited a durable clinical benefit demonstrated a significantly higher infiltration of T cells, as determined through transcriptomic deconvolution methodologies, compared to those without DCB. Notably, despite no marked differences in total CD8+ T cell infiltration across various detection platforms, tumors in the DCB group harbored a higher frequency of CD8+PD1+ T cells. This observation underscores the potential importance of an exhausted or activated CD8+ T cell subset as a biomarker predictive of immunotherapy response, highlighting the nuanced roles of T cell functional states within the tumor milieu.
The research team further explored immune-tumor interactions by evaluating expression levels of major histocompatibility complex class I molecules. Immunohistochemical analysis revealed a trend favoring elevated HLA-I protein expression in tumors from the responsive cohort, with RNA expression data showing particularly robust differences in HLA-B alleles. These findings suggest that enhanced antigen presentation capacity via MHC-I pathways could be instrumental in enabling effective recognition and cytotoxic responses from CD8+ T cells. Interestingly, tumors with lower HLA-I levels corresponded to a relative increase in natural killer (NK) cells, although absolute NK infiltration did not differ significantly, hinting at compensatory innate immune dynamics in less responsive tumors.
MHC class II-dependent immunity emerged as a pivotal correlate of therapeutic outcome. The study reports significantly higher baseline protein levels of pan-HLA-II, along with increased transcription of multiple MHC-II genes, in tumors from patients who achieved DCB. This enhanced MHC-II expression aligns with a pronounced upregulation of T helper 1 (TH1) cell-associated markers such as TBX21 and CXCR3, and importantly, the key immunomodulatory cytokine IFNG (interferon gamma). Such a cytokine milieu potentially fosters an immune-permissive microenvironment, further complemented by elevated PD-L1 expression both transcriptionally and at the protein level, indicative of active immune checkpoint engagement.
A strong functional cytotoxic immune signature was corroborated by elevated levels of granzyme family members (GZMA, GZMB, and GZMK) in tumor secretomes and RNA sequencing datasets, pointing to the presence of active cytolytic effector cells capable of targeting malignancies effectively. These observations underscore the complex interplay between antigen presentation, cytokine signaling, and cytotoxic effector function as cornerstones of an effective anti-tumor immune response.
Beyond CD8+ cytotoxic T lymphocytes, the study highlights the enrichment of follicular helper T (TFH) cells within tumors of responders. Markers characteristic of TFH biology, including BCL6, CXCR5, and CXCL13, were significantly elevated, suggesting that these specialized CD4+ T cells may facilitate effective B cell-mediated immunity. Supporting this notion, B cell transcriptional signatures, increased CD20 protein expression, and markers of plasma cell differentiation such as CD38 and PRDM1 were also augmented in tumors exhibiting DCB. This coordinated activation of both T and B cell compartments may represent a critical axis of tumor immune surveillance and elimination.
Intriguingly, the data reveals a positive correlation between CD8+ T cell and CD20+ B cell infiltrates, and the presence of tertiary lymphoid structures (TLSs) within tumors further coincided with elevated CD8+ T cell infiltration. While TLS detection demonstrated high specificity for DCB, its sensitivity remained limited, indicating that other immune features are also critical to therapeutic success. These findings strengthen the idea that robust and spatially organized adaptive immune responses within the tumor microenvironment are beneficial for clinical outcomes.
Longitudinal analyses following treatment initiation revealed a rapid intensification of these pre-existing immune features in patients with DCB. Three weeks post-therapy, these tumors displayed increases in helper T cells, plasma cell markers, and CD8+ T cell infiltration across multiple analytical platforms. Enhanced activation was evidenced by higher frequencies of HLA-DR+ and CD39+ CD8+ T cells, accompanied by augmented IFNγ production and granzyme expression within the tumor bed, establishing a dynamic immune amplification process post immunotherapy.
Histopathological examination at this early treatment timepoint revealed a significant reduction in cancer cell content paired with increased necrosis and stromal deposition in responsive tumors. Such tissue remodeling may reflect efficient immune-mediated tumor eradication, further emphasizing the biological impact of checkpoint blockade in these patients.
In a holistic view, the study illustrates that successful combination immunotherapy hinges upon an existing, albeit latent, adaptive immune response characterized by robust MHC class I and II antigen presentation, coordinated TH1 and TFH CD4+ T cell responses, active cytotoxic T lymphocytes, and a thriving B cell compartment. The observed rapid reactivation and expansion of these immune constituents early after treatment initiation delineate a mechanistic framework for durable clinical benefit.
To elucidate mechanisms underpinning treatment resistance, the authors also probed the immunosuppressive constituents within the tumor microenvironment. Notably, regulatory T cells (Tregs) and M2-like macrophages were found to be abundant in tumors from patients who responded to therapy, suggesting a nuanced role for these populations in modulating immune responses. These findings challenge classical models of unidirectional immunosuppression by Tregs and macrophages, hinting that their presence may relate to robust immune regulation necessary for effective antitumor immunity.
Collectively, this comprehensive profiling underscores the imperative of considering both immunostimulatory and immunoregulatory elements within the tumor microenvironment when designing and evaluating immunotherapeutic strategies. Furthermore, it advocates for personalized assessment of immune contexture to predict and enhance patient responses in the era of precision oncology.
Given the promising associations uncovered between immune signatures and clinical efficacy, future investigations may refine biomarkers to stratify patients for tailored checkpoint blockade regimens. In addition, these insights pave the way for innovative combination approaches incorporating agents targeting immune suppressor subsets to overcome resistance and optimize therapeutic benefits.
This landmark study advances our understanding of the complex immunological underpinnings of anti-CTLA4 and anti-PD1 combination therapy, offering a roadmap to harness and amplify endogenous adaptive immunity for transformative cancer treatment.
Subject of Research: Immune features associated with efficacy of combined intratumoural anti-CTLA4 and intravenous anti-PD1 immunotherapy in cancer.
Article Title: Safety and efficacy of intratumoural anti-CTLA4 with intravenous anti-PD1.
Article References:
Tselikas, L., Susini, S., Texier, M. et al. Safety and efficacy of intratumoural anti-CTLA4 with intravenous anti-PD1. Nature (2026). https://doi.org/10.1038/s41586-026-10341-w
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