Chitosan hydrogel containing GMCSF and a cancer drug exerts synergistic anti-tumor effects via the induction of CD8+ T cell-mediated anti-tumor immunity

Purpose: Chemo-immunotherapy combinations are limited by systemic immunotoxicity from cancer drugs and rapid clearance of low-molecular-weight drugs after intratumoral injection. A local, biodegradable delivery system was needed to sustain drug/GMCSF exposure at the tumor site, reduce systemic toxicity, and promote tumor antigen cross-presentation and CD8+ T cell-mediated anti-tumor immunity.

Hypothesis: If GMCSF and a cancer drug are co-delivered intratumorally in a chitosan hydrogel, then local tumor cell death will release tumor antigens without severe systemic cytotoxicity, GMCSF will recruit/mature antigen-presenting cells, and the resulting tumor antigen-specific CD8+ T cell response will produce synergistic anti-tumor effects greater than either agent alone.

Aims: Evaluate the anti-tumor efficacy of chitosan hydrogel (CH) containing a cancer drug—doxorubicin (DOX), cisplatin (CDDP), or cyclophosphamide (CTX)—with or without GMCSF in an HPV-16 E7-expressing TC-1 murine tumor model. - Determine whether CH co-delivery of cancer drug + GMCSF induces an E7-specific CD8+ T cell immune response. - Identify the lymphocyte subsets responsible for the anti-tumor effect using in vivo antibody depletion. - Assess systemic toxicity via body-weight changes and local tolerability.

Delivery system: Platform: Thermosensitive, injectable chitosan hydrogel (CH) formed with β-glycerophosphate (β-GP), designed to gel at body temperature and physiological pH after intratumoral injection. - Chitosan properties: Medium molecular weight 161 kDa, viscosity 200,000 cps, 80% deacetylation; 40 mg chitosan dissolved in 1.8 mL 0.1 M HCl. - Payload: Cancer drug (DOX, CDDP, or CTX) plus GMCSF. - Doses used for tumor treatment: 1.25 mg DOX/kg, 1.25 mg CDDP/kg, or 25 mg CTX/kg; with or without 50 mg GMCSF (as reported in the tumor-treatment section). - Controls: CH alone, CH-GMCSF, and CH–cancer drug alone.

Approach: Model: Female C57BL/6 mice, 5–6 weeks old, ~20 g, 5 mice per group. - Tumor: TC-1 murine cervical cancer cells expressing HPV-16 E7; 5 × 10^5 cells in 20 µL injected subcutaneously. - Treatment: On days 7 and 14 after tumor inoculation, 100 µL CH formulation injected intratumorally. - Readouts: Tumor volume measured for ~22 days; body weight measured as toxicity indicator. - Immune analysis: Splenocytes harvested 8 days after final treatment. - Depletion study: Anti-CD4 (GK1.5), anti-CD8 (2.43), or anti-NK1.1 (PK136) antibodies initiated after the second treatment and continued to study end; depletion confirmed >90–95%.

Key methods: Tumor volume by caliper: width × length² / 2. - Body-weight monitoring for systemic toxicity. - Flow cytometry for CD8 surface staining and intracellular IFN-γ staining after overnight stimulation with E7 peptide (aa 49–57; RAH-YNIVTF). - In vivo antibody depletion to determine the contribution of CD8+, CD4+, and NK cells. - Statistical analysis: one-way ANOVA with Tukey–Kramer multiple comparison test, Student’s t-test; P < 0.05 considered significant.

Key results: Tumor growth: CH containing cancer drug + GMCSF significantly reduced TC-1 tumor growth compared with CH–cancer drug alone, CH-GMCSF, or CH alone. CTX was the most potent drug in combination with GMCSF. Fig. 1 reported P < 0.05 for DOX/CDDP + GMCSF and P < 0.01 for CTX + GMCSF versus corresponding CH–drug groups. - Toxicity: CH-GMCSF did not reduce body weight; body weights were maintained or slightly increased with or without cancer drug. No severe local side effects such as pus or inflammation were observed. - Immune response: Intratumoral CH–cancer drug + GMCSF significantly increased E7-specific IFN-γ-secreting CD8+ T cells compared with CH–cancer drug alone. CTX + GMCSF generated the greatest number of E7-specific CD8+ T cells; Fig. 3 showed P < 0.02 for CDDP + GMCSF and P < 0.01 for CTX + GMCSF. - Depletion: CD8+ T cell depletion abolished the anti-tumor effect of CH-CTX + GMCSF, producing tumor volumes nearly identical to CH-CTX control. NK depletion caused a slight increase in tumor volume. CD4 depletion did not significantly change tumor mass. Thus, CD8+ T cells were essential; NK cells may contribute modestly.

Interpretation: Co-treatment with GMCSF and a cancer drug incorporated into a chitosan hydrogel produces synergistic anti-tumor effects via induction of tumor antigen-specific CD8+ T cell-mediated anti-tumor immunity. The biodegradable hydrogel system enables local co-delivery of an immunoadjuvant and an anti-cancer drug, supporting a chemo-immunotherapeutic strategy that may reduce systemic immunotoxicity while enhancing cross-presentation and CD8+ T cell priming.

Limitations: The authors note that a pharmacokinetic study is needed to understand the precise release and action mechanism of the CH system after intratumoral injection. - The reason CTX was more effective than DOX or CDDP was not clarified. - Findings are from a single mouse tumor model (TC-1), with small group sizes (n = 5) and short follow-up (~22–25 days). - The paper notes significant differences between mouse and human immune systems, so extrapolation to humans requires caution. - Clinical applicability requires further studies.