Preclinical safety and biodistribution of adenovirus-based cancer vaccines after intradermal delivery

Controlling timing and location in vaccines

Vaccines are one of the most powerful technologies supporting public health. The adaptive immune response induced by immunization arises following appropriate activation and differentiation of T and B cells in lymph nodes. Among many parameters impacting the resulting immune response, the presence of antigen and inflammatory cues for an appropriate temporal duration within the lymph nodes, and further within appropriate subcompartments of the lymph nodes– the right timing and location– play a critical role in shaping cellular and humoral immunity. Here we review recent advances in our understanding of how vaccine kinetics and biodistribution impact adaptive immunity, and the underlying immunological mechanisms that govern these responses. We discuss emerging approaches to engineer these properties for future vaccines, with a focus on subunit vaccines.

Skin immunisation activates an innate lymphoid cell-monocyte axis regulating CD8+ effector recruitment to mucosal tissues

CD8⁺ T cells provide a critical defence from pathogens at mucosal epithelia including the female reproductive tract (FRT). Mucosal immunisation is considered essential to initiate this response, however this is difficult to reconcile with evidence that antigen delivered to skin can recruit protective CD8⁺ T cells to mucosal tissues. Here we dissect the underlying mechanism. We show that adenovirus serotype 5 (Ad5) bio-distributes at very low level to non-lymphoid tissues after skin immunisation. This drives the expansion and activation of CD3^- NK1.1⁺ group 1 innate lymphoid cells (ILC1) within the FRT, essential for recruitment of CD8⁺ T-cell effectors. Interferon gamma produced by activated ILC1 is critical to licence CD11b⁺Ly6C⁺ monocyte production of CXCL9, a chemokine required to recruit skin primed CXCR3⁺ CD8⁺T-cells to the FRT. Our findings reveal a novel role for ILC1 to recruit effector CD8⁺ T-cells to prevent virus spread and establish immune surveillance at barrier tissues.

Preclinical Evaluation of a Replication-Deficient Recombinant Adenovirus Serotype 5 Vaccine Expressing Guanylate Cyclase C and the PADRE T-helper Epitope

There is an unmet need for improved therapeutics for colorectal cancer, the second leading cause of cancer mortality worldwide. Adjuvant chemotherapy only marginally improves survival in some patients and has no benefit in others, underscoring the clinical opportunity for novel immunotherapeutic approaches to improve survival in colorectal cancer. In that context, guanylate cyclase C (GUCY2C) is an established biomarker and therapeutic target for metastatic colorectal cancer with immunological characteristics that promote durable antitumor efficacy without autoimmunity. Preliminary studies established non-replicating human type 5 adenovirus (Ad5) expressing GUCY2C as safe and effective to induce GUCY2C-specific immune responses and antitumor immunity in mice. This study characterized the biodistribution, immunogenicity, and safety of a vector expressing GUCY2C fused with the human CD4⁺ T helper cell epitope PADRE (Ad5-GUCY2C-PADRE) to advance this vaccine into clinical trials in colorectal cancer patients. Ad5-GUCY2C-PADRE levels were highest in the injection site and distributed in vivo primarily to draining lymph nodes, the liver, spleen and, unexpectedly, to the bone marrow. Immune responses following Ad5-GUCY2C-PADRE administration were characterized by PADRE-specific CD4⁺ T-cell and GUCY2C-specific B-cell and CD8⁺ T-cell responses, producing antitumor immunity targeting GUCY2C-expressing colorectal cancer metastases in the lungs, without acute or chronic autoimmune or other toxicities. Collectively, these data support Ad5-GUCY2C-PADRE as a safe and effective vaccination strategy in preclinical models and position Ad5-GUCY2C-PADRE for Phase I clinical testing in colorectal cancer patients.

Polyamine-blocking therapy reverses immunosuppression in the tumor microenvironment

Correcting T-cell immunosuppression may unleash powerful antitumor responses; however, knowledge about the mechanisms and modifiers that may be targeted to improve therapy remains incomplete. Here, we report that polyamine elevation in cancer, a common metabolic aberration in aggressive lesions, contributes significantly to tumor immunosuppression and that a polyamine depletion strategy can exert antitumor effects that may also promote immunity. A polyamine-blocking therapy (PBT) that combines the well-characterized ornithine decarboxylase (ODC) inhibitor difluoromethylornithine (DFMO) with AMXT 1501, a novel inhibitor of the polyamine transport system, blocked tumor growth in immunocompetent mice but not in athymic nude mice lacking T cells. PBT had little effect on the proliferation of epithelial tumor cells, but it increased the number of apoptotic cells. Analysis of CD45(+) tumor immune infiltrates revealed that PBT decreased levels of Gr-1(+)CD11b(+) myeloid suppressor cells and increased CD3(+) T cells. Strikingly, in a model of neoadjuvant therapy, mice administered with PBT one week before surgical resection of engrafted mammary tumors exhibited resistance to subsequent tumor rechallenge. Collectively, our results indicate that therapies targeting polyamine metabolism do not act exclusively as antiproliferative agents, but also act strongly to prevent immune escape by the tumor. PBT may offer a general approach to heighten immune responses in cancer.

Process development and production of cGMP grade Melan-A for cancer vaccine clinical trials

Melan-A is a cancer testis antigen commonly found in melanoma, and has been shown to stimulate the body's immune response against cancerous cells. We have developed and executed a process utilizing current good manufacturing practices (cGMP) to produce the 6 times-His tagged protein in C41DE3 Escherichia coli for use in Phase I clinical trials. Approximately 11 g of purified Melan-A were produced from a 20 L fed-batch fermentation. Purification was achieved through a three column process utilizing immobilized metal affinity, anion exchange, and cation exchange chromatography with a buffer system optimized for low-solubility, high LPS binding capacity proteins. The host cell proteins, residual DNA, and endotoxin concentration were well below limits for a prescribed dose with a final purity level of 91%.

Phase 1 studies of the safety and immunogenicity of electroporated HER2/CEA DNA vaccine followed by adenoviral boost immunization in patients with solid tumors

BACKGROUND

DNA electroporation has been demonstrated in preclinical models to be a promising strategy to improve cancer immunity, especially when combined with other genetic vaccines in heterologous prime-boost protocols. We report the results of 2 multicenter phase 1 trials involving adult cancer patients (n=33) with stage II-IV disease.

METHODS

Patients were vaccinated with V930 alone, a DNA vaccine containing equal amounts of plasmids expressing the extracellular and trans-membrane domains of human HER2, and a plasmid expressing CEA fused to the B subunit of Escherichia coli heat labile toxin (Study 1), or a heterologous prime-boost vaccination approach with V930 followed by V932, a dicistronic adenovirus subtype-6 viral vector vaccine coding for the same antigens (Study 2).

RESULTS

The use of the V930 vaccination with electroporation alone or in combination with V932 was well-tolerated without any serious adverse events. In both studies, the most common vaccine-related side effects were injection site reactions and arthralgias. No measurable cell-mediated immune response (CMI) to CEA or HER2 was detected in patients by ELISPOT; however, a significant increase of both cell-mediated immunity and antibody titer against the bacterial heat labile toxin were observed upon vaccination.

CONCLUSION

V930 vaccination alone or in combination with V932 was well tolerated without any vaccine-related serious adverse effects, and was able to induce measurable immune responses against bacterial antigen. However, the prime-boost strategy did not appear to augment any detectable CMI responses against either CEA or HER2.

TRIAL REGISTRATION

Study 1 - ClinicalTrials.gov, NCT00250419; Study 2 - ClinicalTrials.gov, NCT00647114.

Selective transduction of dendritic cells in human lymph nodes and superior induction of high-avidity melanoma-reactive cytotoxic T cells by a CD40-targeted adenovirus

Targeted delivery of tumor antigen genes to dendritic cells (DCs) using adenoviral (Ad) vectors holds great potential for cancer immunotherapy. We previously showed that CD40 targeting of Ad vectors enhanced specific transduction of DC in human skin, while simultaneously ensuring their stable maturation and superior allogeneic T-cell stimulatory capacity. In this study, we evaluated whether CD40-targeted Ad encoding the full-length melanoma antigen recognized by T cells-1 (CD40-Ad-MART-1) could be used to efficiently and selectively transduce conventional and plasmacytoid DC to prime melanoma-specific CD8(+) T-effector cells in human melanoma-draining sentinel lymph nodes (SLNs). CD40 targeting of Ad was achieved using a bispecific fusion protein, binding and neutralizing the Ad fiber knob through soluble coxsackie and adenovirus receptor while retargeting the virus to hCD40 through the tumor necrosis factor-like domain of mCD40L. Selective transduction of conventional and plasmacytoid DC subsets by CD40-Ad was observed in suspensions of human melanoma-draining SLN. Moreover, CD40-Ad-MART-1 enhanced the expansion of functional MART-1-specific CD8(+) T cells from SLN with concomitant decreases in CD4:CD8 T-cell ratios and CD4(+)CD25(hi)FoxP3(+) regulatory T-cell rates. Additional studies revealed that transduction and activation of monocyte-derived DCs with CD40-Ad-MART-1 significantly enhanced their priming efficiency of functional CD8(+) effector T cells with high avidity. These findings provide preclinical evidence of possible efficacy of this approach for cancer immunotherapy.

Evaluation of biodistribution and safety of adenovirus vector containing MDR1 in mice

Background

The aim of this study is to examine the safety and distribution of Ad-EGFP-MDR1, an adenovirus encoding human multidurg resistance gene (human MDR1), in the mice colon carcinoma model.

Methods

After bone marrow cells (BMCs) were infected with Ad-EGFP-MDR1, they were administered by intra bone marrow-bone marrow transplantation (IBM-BMT). Total adenovirus antibody and serum adenovirus neutralizing factor (SNF) were determined. Biodistribution of Ad-EGFP-MDR1 was detected by in situ hybridization and immunohistochemistry. The peripheral hematocyte white blood cell (WBC), haemoglobin (Hb), red blood cell (RBC) and platelet (Plt) counts were analyzed.

Results

Neither total adenovirus antibody nor SNF increased weeks after BMT. In situ hybridization and immunohistochemistry demonstrated concordant expression of human MDR1 and P-gp which were found in lung, intestine, kidney and BMCs after BMT, but not detected in liver, spleen, brain and tumor. No significant abnormality of the recovery hematocyte was observed on Day 30 after treatment.

Conclusion

The results indicate that IBM-BMT administration of a replication defective adenovirus is a feasible mode of delivery, allowing exogenous transference. The findings in this study are conducted for the future long-term studies of safety assessment of Ad-EGFP-MDR1.

Polarization of protective immunity induced by replication-incompetent adenovirus expressing glycoproteins of pseudorabies virus

Replication-incompetent adenoviruses expressing three major glycoproteins (gB, gC, and gD) of pseudorabies virus (PrV) were constructed and used to examine the ability of these glycoproteins to induce protective immunity against a lethal challenge. Among three constructs, recombinant adenovirus expressing gB (rAd-gB) was found to induce the most potent immunity biased to Th1-type, as determined by the IgG isotype ratio and the profile of the Th1/Th2 cytokine production. Conversely, the gC-expressing adenovirus (rAd-gC) revealed Th2-type immunity and the gD-expressing adenovirus (rAd-gD) induced lower levels of IFN-? and IL-4 production than other constructs, except IL-2 production. Mucosal delivery of rAd-gB induced mucosal IgA and serum IgG responses and biased toward Th2-type immune responses. However, these effects were not observed in response to systemic delivery of rAd-gB. In addition, rAd-gB appeared to induce effective protective immunity against a virulent viral infection, regardless of whether it was administered via the muscular or systemic route. These results suggest that administration of replication-incompetent adenoviruses can induce different types of immunity depending on the expressed antigen and that recombinant adenoviruses expressing gB induced the most potent Th1-biased humoral and cellular immunity and provided effective protection against PrV infection.

Adenoviral vectors for gene therapy

Vectors based on human adenovirus serotypes 2 (Ad2) and 5 (Ad5) of species C possess a number of features that have favored their widespread employment for gene delivery both in vitro and in vivo. However, the use of recombinant Ad2- and Ad5-based vectors for gene therapy also suffers from a number of disadvantages. These vectors possess the tropism of the parental viruses, which infect all cells that possess the appropriate surface receptors, precluding the targeting of specific cell types. Conversely, some cell types that represent important targets for gene transfer express only low levels of the cellular receptors, which lead to inefficient infection. Another major disadvantage of Ad2- and Ad5-based vectors in vivo is the elicitation of both an innate and an acquired immune response. Considerable attention has therefore been focused on strategies to overcome these limitations, thereby permitting the full potential of adenoviral vectors to be realized.