Reengineering dendritic cell-based anti-cancer vaccines

Despite initial enthusiasm, dendritic cell (DC)-based anticancer vaccines have yet to live up to their promise as one of the best hopes for generating effective anti-tumor immunity. One of the principal reasons for the generally disappointing results achieved thus far could be that the full potential of DCs has not been effectively exploited.

Here, we argue that dramatic improvements in vaccine efficacy will probably require a careful re-evaluation of current vaccine design. The formulation of new strategies must take into account the natural history of DCs, particularly their role in helping the immune system deal with infection. Equally critical is the emerging importance of soluble factors, notably interleukin-12, in modulating the quality of immune responses.

Vaccines should also be designed to recruit helper T cells and antibody-producing Bcells rather than simply cytotoxic T lymphocytes. Finally, the judicious selection of tumor, target antigen, and disease stage best suited for treatment should serve as the foundation of trial designs. Our discussion addresses a recent clinical vaccine trial to treat early breast cancer, where many elements of this new strategy were put into practice.

Combining Innate Immunity With Radiation Therapy for Cancer Treatment

The widely shared goal of cancer immunotherapy is to stimulate an immune response of sufficient quality and magnitude to destroy primary malignancies and their metastases. Cancer immunotherapy has taken many cues from the development of successful antimicrobial vaccines.

Antimicrobial vaccines rely on the immune system’s capacity to distinguish self-tissues from infectious non-self so that invading pathogens, and the cells they might infect, could be efficiently identified and eliminated, while sparing healthy tissues. The process of discriminating self from infectious non-self is facilitated by the millions (and in some cases billions) of years of evolutionary divergence that separates vertebrates from the pathogens that infect them.

This separation has given rise to individual proteins and other generalized molecular structures that serve to distinguish microbes from men. In theory, malignant cells that express protein antigens that either are unique to the tumor, vastly over-expressed by the tumor, or whose expression is at least restricted to a narrow range of self-tissues provides a potential immunologic handle whereby tumors may be specifically recognized and destroyed.

In practice, however, it has proven unexpectedly difficult to coax the immune system into vigorously rejecting malignancies, despite repeated demonstrations that tumor-associated antigens can provoke immune responses. In this issue of Clinical Cancer Research, Mason et al. (1) shows, using a murine subcutaneous and lung metastasis sarcomatreatment model, that synthetic oligodeoxynucleotides (ODN) containing unmethylated CpG motifs (characteristic of bacterial DNA) could be given with conventional radiation therapy to greatly augment therapeutic efficacy through an apparent immune-mediated.

A Novel Dendritic Cell-Based Immunization

The immune system has traditionally been divided into two parts; the innate and the adaptive. The innate immune system’s components include monocytes, macrophages, granulocytes, NK and dendritic cells (DC). The adaptive immune system is composed of antibody-producing B lymphocytes, as well as CD4pos helper T cells and CD8pos cytotoxic T cells. These cells work together to sense, control and eliminate infection. Agents of innate immunity identify microbes through special pattern recognition receptors that sense biochemical structures (usually non-proteins) common to broad classes of potential pathogens

(1). On the other hand, T and B lymphocytes specialize in responding against antigens (usually proteins) specific to the individual species of microbe. DCs have a unique role in that they form a critical bridge between innate and adaptive immunity. Pattern recognition proteins belonging to the Toll-like family of transmembrane receptors (2) induce a maturation and migration program whereby various DC populations, including monocytederived DCs, convey peripherally-acquired proteins to T cells located in the regional draining lymph nodes (3).

The DCs “present” the microbial antigens to T cells in the form of processed peptides complexed with self major histocompatibility proteins (4). This supplies an important signal (signal 1) to T cells that, along with maturation-enhanced co-stimulatory molecule (CD80, CD86) expression (signal 2), can fully activate T cells (5). DCs and some other accessory cells can supply so-called “third signals” (6) that often are expressed in the form of soluble factors, for example, IL-12, IL-23, IL-6 and TGF-beta. Such signals can profoundly influence helper T cell development toward discrete functional phenotypes that include IFN-γ-secreting Th1, IL-17- secreting Th17, as well as anti-inflammatory Treg that produce TGF-beta and IL-10 (7–10).

In many instances, the precise combination of activation signals received by DC dictates whether individual 3rd signal agents will be produced, and hence which Th phenotypes will be selectively induced by the DC (11). Although the immune system evolved primarily to deal with infections, it may be possible to direct it against malignancies. An ideal strategy for inducing anti-tumor immunity must successfully accomplish several goals-some of which are overlapping with traditional antimicrobial vaccines, but others unique to the particular requirements of effective anti-tumor immunity. For example, an effective anti-tumor vaccine must overcome the immune system’s natural tendency to resist the development of strong immunity against self-proteins (i.e. tolerance).

It must also generate immunity of a quality and intensity likely to reduce or eliminate tumor burdens. In the case of therapeutic vaccines, immunity must be effectively induced when disease is already firmly established. Finally, such induced immunity should be durable, so that possible tumor recurrences can be suppressed for long per periods postimmunization.

Anti-HER2 CD4(+) T-helper Type 1 Response is a Novel Immune Correlate to Pathologic Response Following Neoadjuvant Therapy in HER2-positive Breast Cancer

A progressive loss of circulating anti-human epidermal growth factor receptor-2/neu (HER2) CD4(+) T-helper type 1 (Th1) immune responses is observed in HER2(pos)-invasive breast cancer (IBC) patients relative to healthy controls. Pathologic complete response (pCR) following neoadjuvant trastuzumab and chemotherapy (T + C) is associated with decreased recurrence and improved prognosis. We examined differences in anti-HER2 Th1 responses between pCR and non-pCR patients to identify modifiable immune correlates to pathologic response following neoadjuvant T + C.

Anti-HER2 Th1 responses in 87 HER2(pos)-IBC patients were examined using peripheral blood mononuclear cells pulsed with 6 HER2-derived class II peptides via IFN-γ ELISPOT. Th1 response metrics were anti-HER2 responsivity, repertoire (number of reactive peptides), and cumulative response across 6 peptides (spot-forming cells [SFC]/10(6) cells). Anti-HER2 Th1 responses of non-pCR patients (n = 4) receiving adjuvant HER2-pulsed type 1-polarized dendritic cell (DC1) vaccination were analyzed pre- and post-immunization.
Depressed anti-HER2 Th1 responses observed in treatment-naïve HER2(pos)-IBC patients (n = 22) did not improve globally in T + C-treated HER2(pos)-IBC patients (n = 65). Compared with adjuvant T + C receipt, neoadjuvant T + C – utilized in 61.5 % – was associated with higher anti-HER2 Th1 repertoire (p = 0.048). While pCR (n = 16) and non-pCR (n = 24) patients did not differ substantially in demographic/clinical characteristics, pCR patients demonstrated dramatically higher anti-HER2 Th1 responsivity (94 % vs. 33 %, p = 0.0002), repertoire (3.3 vs. 0.3 peptides, p < 0.0001), and cumulative response (148.2 vs. 22.4 SFC/10(6), p < 0.0001) versus non-pCR patients. After controlling for potential confounders, anti-HER2 Th1 responsivity remained independently associated with pathologic response (odds ratio 8.82, p = 0.016). This IFN-γ(+) immune disparity was mediated by anti-HER2 CD4(+)T-bet(+)IFN-γ(+) (i.e., Th1) – not CD4(+)GATA-3(+)IFN-γ(+) (i.e., Th2) – phenotypes, and not attributable to non-pCR patients’ immune incompetence, host-level T-cell anergy, or increased immunosuppressive populations. In recruited non-pCR patients, anti-HER2 Th1 repertoire (3.7 vs. 0.5, p = 0.014) and cumulative response (192.3 vs. 33.9 SFC/10(6), p = 0.014) improved significantly following HER2-pulsed DC1 vaccination.

Anti-HER2 CD4(+) Th1 response is a novel immune correlate to pathologic response following neoadjuvant T + C. In non-pCR patients, depressed Th1 responses are not immunologically “fixed” and can be restored with HER2-directed Th1 immune interventions. In such high-risk patients, combining HER2-targeted therapies with strategies to boost anti-HER2 Th1 immunity may improve outcomes and mitigate recurrence.

Affiliation

Department of Surgery, University of Pennsylvania Perelman School of Medicine, Rena Rowen Breast Center, 3400 Civic Center Drive, Philadelphia, PA, 19104, USA.

Radiation as Immunomodulator: Implications for Dendritic Cell-Based Immunotherapy

The last decade has witnessed significant progress in the field of cancer immunotherapy. This has, in part, been driven by a growing recognition that elements of the innate immune response can be harnessed to induce robust immunity against tumor-associated targets. Nonetheless, as clinically effective immunotherapy for the majority of cancers remains a distant goal, attention has shifted toward multimodality approaches to cancer therapy, sometimes combining novel immunotherapeutics and conventional therapeutics. The traditional view of radiation therapy as immunosuppressive has been challenged, prompting a re-evaluation of its potential as an adjunct to, or even a component of immunotherapy. Radiation therapy may enhance expression of tumor-associated antigens, induce targeting of tumor stroma, diminish regulatory T-cell activity and activate effectors of innate immunity such as dendritic cells through Toll-like receptor (TLR)-dependent mechanisms. Here, we review recent progress in the field of dendritic cell-based immunotherapy, evidence for radiation-induced anti-tumor immunity and TLR signaling and the results of efforts to rationally integrate radiation into dendritic cell-based immunotherapy strategies.

Affiliation

A  Department of Surgery, University of Pennsylvania, Philadelphia, Pennsylvania.