*3.3.1 ICT combines with cancer vaccine*

Combined immunotherapies of ICT and cancer vaccine can potentiate antitumor immune response. Kuai et al. developed a nanodisc to co-deliver anti-PD-1 and anti-CTLA-4, in combination with the sHDL-Ag/CpG mediated cancer vaccine, for the MC-38 colon tumors and B16F10 melanomas treatment [41]. The combination of ICT with neoantigen vaccination markedly inhibit tumor growth and eradicate established tumors, suggesting the superiority of combined immunotherapeutic strategy. Zhu et al. further explored this strategy by constructing endogenously self-assembled albumin/AlbiVax nanocomplexes [42]. The AlbiVax nanovaccines are composed of antigens and adjuvants conjugated with maleimide-functionalized Evans Blue (MEB), namely MEB-Ag and MEB-CpG. MEB can bind with endogenous albumin which can work as a natural carrier and enable to direct the nanovaccine trafficking to the lymph nodes. The anti-PD-1 based ICT could prevent exhaustion of CTL responses, in combination with AlbiVax nanovaccine which can efficiently traffic to lymph nodes, leading to induction of robust antitumor immune response. The found that vaccination with AlbiVax led to 12.5% tumors regression, while combination treatment of AlbiVax + anti-PD-1 increased tumor regression to 60% in mice.

### *3.3.2 ICT combines with chemotherapy*

It has been realized that cytotoxic chemotherapy exerts therapeutic effects not only through direct tumor cells killing, but also may be related with immunoregulatory properties of chemotherapeutic agents. The chemotherapy achieve antitumor effects by facilitating tumor cell killing or inhibiting tumor cell division via multiple mechanism, such as causing DNA damage, disrupting DNA replication, preventing mitosis, cellular metabolism and microtubule assembly [43]. Although the precise mechanism remains further investigation, it is believed that chemotherapy can modulate T cell activity by promoting immunogenic cell death (ICD), increasing effector T-cell response, enhancing tumor antigenicity, or blocking immune suppressive pathways [44, 45]. Chemotherapy can induce ICD by releasing damage-associated molecular patterns (DAMP), which can be recognized by pattern-recognition receptors such as Toll-like receptors (TLRs) expressed on antigen-presenting cells (APCs). These DAMPs and tumor-associated antigens collectively elicit APCs maturation and induce a robust antitumor immunity. For instance, anthracycline-based chemotherapy has been shown to induce immunogenic cell death (ICD) which favors the DCs maturation and block immunosuppressive pathways in the TME [44]. In a genetically engineered mouse lung adenocarcinoma model, combined therapy of oxaliplatin and cyclophosphamide drive the T cell infiltration-lacking tumors sensitive to ICT based on PD1 and CTLA4 antibodies (**Figure 4**) [46].

#### *3.3.3 ICT combines with radiotherapy*

When ICT combines with radiotherapy, abscopal effect can occur to facilitate regression of distant tumors or metastases. Specifically, APCs uptake tumorassociated antigens (TAAs) released by the dying tumor cells upon irradiation, accumulate to the lymph nodes and activate CD8+ T-cells to eradicate the tumor cells in primary and distant tumors. It has been recognized that the abscopal effect can be augmented by combining radiotherapy with ICT. Ni et al. established a radiosensitizer (Hf12-DBA) for radiotherapy in combination with anti-PD-L1 based ICT, resulting antitumor response both in primary and distant tumors [47]. In dual subcutaneous colorectal CT26 tumors bearing mice, monotherapies of ICT and radiotherapy just lead to delayed primary and distant tumors growth, while combination of ICT and radiotherapy elicit complete regression of primary, treated tumor and shrinkage of

#### **Figure 4.**

*Scheme illustration showing the cancer treatment with chemotherapy which can elicit immune stimulation including: Secretion of ATP; expression of type 1 interferon (IFN); exposure of calreticulin (CALR) on the outer membrane; and release of high mobility group box 1 (HMGB1).*

#### *Immune Checkpoint and Tumor Therapy DOI: http://dx.doi.org/10.5772/intechopen.107203*

distant, non-irradiated tumors. Accordingly, the abscopal effect was boosted and the antitumor immune responses was potentiated by the combination of ICT and radiotherapy. Min et al. developed a new strategy to improve abscopal effect by constructing antigen-capturing NPs mediated combination therapy of anti-PD-1-based ICT and radiotherapy [48]. In bilateral B16F10 melanomas bearing mice, ICT and radiotherapy combination therapy mediated by antigen-capturing NPs induced a 20% complete response rate and tumor re-challenge resistant 3 months later. By contrast, mice receiving the combination treatment without antigen-capturing succumbed to disease within 40 days, suggesting that antigen-capturing strategy play a critical role in improving the abscopal effect and enhance therapeutic effects.

#### *3.3.4 ICT combines with phototherapy*

Combination of phototherapy can induce abscopal effect, reduce tumor burden, and boost antitumor responses in various tumor models. Phototherapy relies on photosensitizers which can generate reactive oxygen species for photodynamic therapy (PDT) or heat for photothermal therapy (PTT) upon laser irradiation to eradicate tumor cells. Chen et al. combined PLGA-ICG-R837-based PTT with anti-CTLA-4 based ICT to induce robust anti-tumor immune responses for cancer immunotherapy [49]. In a 4 T1 breast tumor model with lung metastases, the combination treatment of PTT and ICT could protect treated mice against tumor rechallenging 40 days post ablation, while surgery + anti-CTLA-4 treatment or PLGA-ICG-R837-based-PTT alone can lead to metastases.

#### *3.3.5 Challenges for combination therapies*

Combination therapy is crucial for increasing sensitivity of ICT and enhancing antitumor efficacy. However, there are still some challenges need to be addressed. First, careful consideration needs to be given to for which therapies to combine. Preclinically determining whether there is an additive or synergistic therapeutic effect and determining the optimal combination can help identify and drive combinations that produce synergistic therapeutic effects into clinical trials. Second, strong rationale is needed for the spatiotemporal factors of combination therapy administration. The half-life, tumor accumulation and kinetics for each monotherapy should be examined. Nanotechnology exhibit superiorities in this aspect by integrating multiple therapies into a single platform to promote accumulation and co-localization at the target sites. Additionally, optimizing the dose and scheduling of combination therapy is also needed when considering spatiotemporal factors. Of note, nanotechnology shows the potential to solve the challenges related to combination therapy in a number of ways: through integrating multiple therapies into a single nanoplatform, or optimizing dosage and therapeutic schedule, or exploring the potential therapeutic mechanisms.
