Cancer Immunotherapy: Checkpoint Inhibitors, CAR-T, and Vaccines

Cancer immunotherapy has fundamentally reshaped oncology over the past fifteen years, converting several formerly terminal diagnoses into conditions where long-term, durable remission is now achievable. Unlike chemotherapy or radiotherapy — which kill tumor cells directly — cancer immunotherapy works with the patient's own immune system, training or unleashing it to seek and destroy malignant cells throughout the body. Four overlapping pillars define modern cancer immunotherapy: immune checkpoint inhibitors, chimeric antigen receptor (CAR) T-cell therapy, therapeutic cancer vaccines, and tumor-infiltrating lymphocyte (TIL) therapy. Each attacks cancer through a distinct immunological mechanism, and together they define the therapeutic frontier of oncology.

Immune Checkpoint Inhibitors: Releasing the Brakes on Antitumor Immunity

The T-cell immune response is regulated by co-inhibitory receptor–ligand pairs that evolved to prevent autoimmunity. Tumors exploit these checkpoints to suppress antitumor immunity. Checkpoint inhibitor therapy blocks this exploitation, restoring T-cell effector function within the tumor microenvironment. Three checkpoint axes have now been clinically validated:

• CTLA-4 (CD152): Cytotoxic T-lymphocyte-associated protein 4 suppresses T-cell activation at the priming stage in lymph nodes by competing with CD28 for B7 ligands (CD80/CD86). Ipilimumab (Yervoy), a fully human IgG1 anti-CTLA-4 monoclonal antibody, was the first checkpoint inhibitor approved by the FDA (March 2011) for unresectable or metastatic melanoma. In the pivotal phase III trial, ipilimumab improved median overall survival to 10.1 months versus 6.4 months with the gp100 vaccine comparator, with durable responses in a subset of patients — the first agent to improve overall survival in metastatic melanoma (Hodi et al., N Engl J Med 2010).
• PD-1/PD-L1 axis: Programmed death-1 (PD-1/CD279) is expressed on exhausted T cells within the tumor microenvironment. Its ligands, PD-L1 (CD274/B7-H1) and PD-L2, are upregulated on tumor cells and stromal cells, directly suppressing effector T-cell function at the tumor site. Anti-PD-1 antibodies pembrolizumab (Keytruda) and nivolumab (Opdivo), along with anti-PD-L1 antibodies atezolizumab (Tecentriq) and durvalumab (Imfinzi), have collectively received approvals across more than 15 tumor types, including non-small-cell lung cancer (NSCLC), melanoma, renal cell carcinoma, MSI-H/dMMR solid tumors, and head and neck squamous cell carcinoma. A landmark tissue-agnostic approval was granted in June 2020: pembrolizumab for any solid tumor with high tumor mutational burden (TMB-H, ≥10 mutations/megabase), the first biomarker-driven pan-tumor approval based on the KEYNOTE-158 study (Marabelle et al., Lancet Oncol 2020). PD-L1 expression, quantified by immunohistochemistry as tumor proportion score (TPS) or combined positive score (CPS), serves as a companion diagnostic for pembrolizumab across several indications.
• LAG-3 (CD223): Lymphocyte-activation gene 3 is a third inhibitory checkpoint co-expressed with PD-1 on exhausted tumor-infiltrating T cells. Dual LAG-3 and PD-1 blockade produces synergistic reinvigoration of T-cell exhaustion. The fixed-dose combination of relatlimab (anti-LAG-3) and nivolumab (anti-PD-1), marketed as Opdualag, received FDA approval in March 2022 for unresectable or metastatic melanoma — the first approved LAG-3 inhibitor. In the RELATIVITY-047 phase II/III trial, relatlimab–nivolumab extended median progression-free survival to 10.1 months versus 4.6 months with nivolumab alone (HR 0.75; p=0.006) (Tawbi et al., N Engl J Med 2022). Additional next-generation checkpoints under active clinical investigation include TIM-3 (HAVCR2), TIGIT, and VISTA.

CAR-T Cell Therapy: Engineering Precision Killers

Chimeric antigen receptor (CAR) T-cell therapy is a form of adoptive cell transfer in which a patient's own T cells are genetically engineered ex vivo to express a synthetic receptor targeting a tumor-associated antigen, then reinfused to hunt malignant cells. The CAR structure consists of an extracellular single-chain variable fragment (scFv) antigen-binding domain, a transmembrane linker, and an intracellular signaling module combining CD3ζ with one or two costimulatory domains (CD28 or 4-1BB/CD137). Generation evolution has improved T-cell persistence and effector function:

• 1st generation: CD3ζ signaling only — short persistence, limited efficacy.
• 2nd generation: CD3ζ + single costimulatory domain (CD28 or 4-1BB) — the architecture of all currently approved CAR-T products.
• 3rd generation: CD3ζ + dual costimulatory domains — under investigation.
• 4th generation ("armored" CARs): Engineered to secrete pro-inflammatory cytokines (e.g., IL-12) in the tumor microenvironment to reshape the immunosuppressive niche.

Six CAR-T products have received FDA approval:

• Tisagenlecleucel (tisa-cel, Kymriah) — CD19-targeted, approved for pediatric/young adult B-cell ALL and diffuse large B-cell lymphoma (DLBCL). In the ELIANA trial, 81% of pediatric patients with relapsed/refractory B-ALL achieved overall remission (Maude et al., N Engl J Med 2018).
• Axicabtagene ciloleucel (axi-cel, Yescarta) — CD19-targeted, approved for relapsed/refractory DLBCL and follicular lymphoma.
• Lisocabtagene maraleucel (liso-cel, Breyanzi) — CD19-targeted, approved for large B-cell lymphoma.
• Idecabtagene vicleucel (ide-cel, Abecma) and ciltacabtagene autoleucel (cilta-cel, Carvykti) — both BCMA-targeted, approved for relapsed/refractory multiple myeloma.
• Brexucabtagene autoleucel (brexu-cel, Tecartus) — CD19-targeted, approved for mantle cell lymphoma and adult B-ALL.

Extending CAR-T therapy to solid tumors remains a major scientific challenge. Barriers include poor T-cell trafficking to the tumor, antigen heterogeneity and loss, and immunosuppression within the tumor microenvironment (TGF-β, IL-10, VEGF, MDSC accumulation). Emerging strategies include target combinations, locoregional delivery, and co-expressing checkpoint-blocking payloads.

Cancer Vaccines and Tumor-Infiltrating Lymphocyte Therapy

Unlike prophylactic vaccines against infectious agents, therapeutic cancer vaccines are administered after cancer diagnosis to stimulate or amplify tumor-specific immune responses. Sipuleucel-T (Provenge), an autologous dendritic cell-based vaccine targeting prostatic acid phosphatase (PAP), became the first FDA-approved therapeutic cancer vaccine in April 2010 for asymptomatic or minimally symptomatic metastatic castration-resistant prostate cancer.

The emergence of personalized mRNA neoantigen vaccines represents a major advance. These vaccines are manufactured individually for each patient by sequencing the tumor genome, identifying patient-specific somatic mutations predicted to generate immunogenic neoantigens, and encoding up to 34 neoantigen sequences in a lipid-nanoparticle mRNA construct. In the KEYNOTE-942 Phase IIb trial, mRNA-4157/V940 combined with pembrolizumab demonstrated a statistically significant reduction in recurrence or death versus pembrolizumab alone in stage III/IV melanoma after resection, establishing proof-of-concept for individualized neoantigen vaccination in solid tumors. Phase III evaluation is ongoing.

Tumor-infiltrating lymphocyte (TIL) therapy involves surgically harvesting TILs from the patient's resected tumor, rapidly expanding them ex vivo to billions of polyclonal tumor-reactive T cells, and reinfusing them after lymphodepleting chemotherapy. Lifileucel (Amtagvi) received FDA approval in February 2024 as the first TIL therapy, indicated for adult patients with unresectable or metastatic melanoma previously treated with anti-PD-1 therapy and, if BRAF V600E/K mutated, a BRAF inhibitor.

The Tumor Microenvironment: A Key Battleground for Immunotherapy

Solid tumors exist within a complex cellular ecosystem called the tumor microenvironment (TME), which is often profoundly immunosuppressive and constitutes a major barrier to durable immunotherapy responses. The TME is composed of cancer cells, tumor-infiltrating lymphocytes (TILs), myeloid-derived suppressor cells (MDSCs), tumor-associated macrophages (TAMs, frequently polarized to the pro-tumoral M2 phenotype), cancer-associated fibroblasts (CAFs), NK cells, regulatory T cells (Tregs), and endothelial cells. The interplay of these compartments determines whether an immune response can be initiated and sustained — the Cancer-Immunity Cycle framework (Chen & Mellman, Immunity 2013).

Key immunosuppressive mechanisms in the TME include:

• PD-L1 upregulation on tumor cells and TAMs, directly suppressing CD8⁺ T-cell effector function via PD-1 ligation.
• TGF-β secretion by CAFs and Tregs, suppressing T-cell proliferation and promoting immune exclusion at tumor margins.
• VEGF-mediated immunosuppression: VEGF impairs dendritic cell maturation and promotes endothelial anergy, reducing T-cell extravasation into the tumor.
• IDO1 pathway: Tryptophan catabolism by IDO1 generates immunosuppressive kynurenines that inhibit T-cell function and expand Tregs.
• MDSC and Treg accumulation: Both cell types suppress effector T-cell responses via distinct mechanisms including arginase-1, ROS, and IL-10/TGF-β secretion.

Quantifying the immunological state of the TME is essential for predicting checkpoint inhibitor response and developing rational combination strategies. BioHippo's catalog includes a comprehensive suite of validated ELISA kits for TME profiling — including PD-L1/CD274, PD-1/PDCD1, CTLA-4, LAG-3, TIM-3/HAVCR2, TIGIT, TGF-β1, VEGF, IFN-γ, granzyme B, and cytokine panels — enabling quantitative characterization of both immunosuppressive and effector-immune axes across human, mouse, and rat sample types.

BioHippo Cancer Immunotherapy Research Tools

Advancing cancer immunotherapy research requires precise, validated tools for quantifying the molecular mediators of immune activation and suppression. BioHippo offers one of the broadest checkpoint immunology reagent portfolios available from a single supplier:

• Checkpoint protein ELISA kits: PD-L1 (CD274), PD-1 (PDCD1), CTLA-4 (CD152), LAG-3 (CD223), TIM-3 (HAVCR2), PD-L2 (PDCD1LG2), TIGIT — available for human, mouse, and rat; multiple formats including PicoKine^®, Quick ELISA, and EZ-Set^™ DIY antibody pairs.
• Cytokine and effector molecule ELISA kits: IFN-γ, TNF-α, IL-6, IL-10, IL-2, TGF-β1, VEGF-A — critical for characterizing T-cell activation and TME immunosuppression.
• Cytotoxicity markers: Granzyme B (GZMB), Granzyme A (GZMA), and perforin (PRF1) antibodies and ELISA kits for quantifying CD8⁺ T-cell and NK cell cytotoxic activity.
• Primary antibodies: Validated anti-human and anti-mouse antibodies targeting checkpoint receptors, costimulatory molecules, and TME markers. Browse the full primary antibodies collection.

Browse the full ELISA kit collection or search for checkpoint immunology products to find the right assay for your research model.

Frequently Asked Questions

What is cancer immunotherapy?

Cancer immunotherapy is a broad class of treatments that harness or enhance the patient's own immune system to recognize and eliminate tumor cells, rather than destroying cells directly with cytotoxic agents. It includes immune checkpoint inhibitors (which remove molecular brakes on T-cell activation), adoptive cell therapies (CAR-T and TIL therapy), therapeutic cancer vaccines, and cytokine-based approaches. Because immunotherapy engages systemic immunological memory, some patients achieve durable responses lasting years after treatment ends — a hallmark that distinguishes it from conventional chemotherapy.

How do PD-1/PD-L1 checkpoint inhibitors work?

PD-1 (programmed death-1) is an inhibitory co-receptor expressed on chronically stimulated, exhausted T cells within the tumor microenvironment. Tumor cells and immunosuppressive stromal cells upregulate PD-L1 (the PD-1 ligand), which engages PD-1 on T cells and delivers an inhibitory signal that suppresses cytokine production, proliferation, and cytotoxic function. Anti-PD-1 antibodies (pembrolizumab, nivolumab) or anti-PD-L1 antibodies (atezolizumab, durvalumab) block this interaction, restoring T-cell effector function and enabling the immune system to kill tumor cells. High PD-L1 expression (measured by TPS or CPS IHC) and high tumor mutational burden (TMB-H) are validated predictive biomarkers for response.

What is CAR-T cell therapy?

CAR-T cell therapy is a personalized form of adoptive cell immunotherapy. T cells are collected from the patient by leukapheresis, genetically engineered to express a chimeric antigen receptor (CAR) targeting a tumor-specific surface antigen (e.g., CD19 in B-cell malignancies, BCMA in multiple myeloma), expanded to billions of cells, and reinfused after lymphodepleting chemotherapy. The CAR combines an extracellular scFv antibody domain for antigen recognition with intracellular signaling domains (CD3ζ, CD28, or 4-1BB) that drive T-cell activation and persistence. FDA-approved CAR-T products targeting CD19 include tisagenlecleucel, axicabtagene ciloleucel, lisocabtagene maraleucel, and brexucabtagene autoleucel; BCMA-targeted products include idecabtagene vicleucel and ciltacabtagene autoleucel for myeloma.

What is the tumor microenvironment in cancer?

The tumor microenvironment (TME) is the complex cellular and molecular ecosystem surrounding and infiltrating a solid tumor. It includes tumor cells, CD8⁺ cytotoxic T cells, CD4⁺ helper T cells, regulatory T cells (Tregs), tumor-associated macrophages (TAMs), myeloid-derived suppressor cells (MDSCs), cancer-associated fibroblasts (CAFs), natural killer cells, and endothelial cells. The balance between pro-inflammatory (immunostimulatory) and immunosuppressive signals within the TME largely determines whether checkpoint inhibitor therapy will succeed. Key immunosuppressive mediators include TGF-β, VEGF, IL-10, IDO1 metabolites, and PD-L1 expression on tumor and stromal cells.

How do mRNA cancer vaccines work?

mRNA cancer vaccines encode tumor neoantigens — mutant peptides arising from patient-specific somatic mutations that are absent from normal tissue — in a lipid-nanoparticle mRNA delivery vehicle. After injection, antigen-presenting cells translate the mRNA and present the neoantigen-derived peptides on MHC molecules, priming neoantigen-specific CD4⁺ and CD8⁺ T cells. Because neoantigens are unique to each patient's tumor, each vaccine is individually manufactured. This personalized approach is being tested in combination with PD-1 checkpoint blockade (e.g., pembrolizumab), with the hypothesis that checkpoint inhibition prevents exhaustion of the newly primed neoantigen-specific T cells. Clinical validation is advancing through Phase III trials in melanoma and other solid tumor types.

References

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2. Topalian SL et al. Safety, activity, and immune correlates of anti-PD-1 antibody in cancer. N Engl J Med. 2012;366(26):2443-54.
3. Tawbi HA et al. Relatlimab and nivolumab versus nivolumab in untreated advanced melanoma. N Engl J Med. 2022;386(1):24-34.
4. Maude SL et al. Tisagenlecleucel in children and young adults with B-cell lymphoblastic leukemia. N Engl J Med. 2018;378(5):439-448.
5. Chen DS, Mellman I. Oncology meets immunology: the cancer-immunity cycle. Immunity. 2013;39(1):1-10.
6. Marabelle A et al. Association of tumour mutational burden with outcomes in patients with advanced solid tumours treated with pembrolizumab: prospective biomarker analysis of KEYNOTE-158. Lancet Oncol. 2020;21(10):1353-1365.