Laser Adjuvant-Assisted Peptide Vaccine Promotes Skin Mobilization of Dendritic Cells and Enhances Protective CD8+ TEM and TRM Cell Responses against Herpesvirus Infection and Disease

Ionic Liquid-Based Transcutaneous Peptide Antitumor Vaccine: Therapeutic Effect in a Mouse Tumor Model

Traditional vaccinations need to be injected with needles, and since some people have a strong aversion to needles, a needle-free alternative delivery system is important. In this study, we employed ionic liquids (ILs) for transcutaneous delivery of cancer antigen-derived peptides to obtain anticancer therapeutic effects in a needle-free manner. ILs successfully increased the in vitro skin permeability of a peptide from Wilms tumor 1 (WT1), one of the more promising cancer antigens, plus or minus an adjuvant, resiquimod (R848), a toll-like receptor 7 agonist. In vivo studies demonstrated that concomitant transcutaneous delivery of WT1 peptide and R848 by ILs induced WT1-specific cytotoxic T lymphocyte (CTL) in mice, resulting in tumor growth inhibition in Lewis lung carcinoma-bearing mice. Interestingly, administrating R848 in ILs before WT1 peptides in ILs increased tumor growth inhibition effects compared to co-administration of both. We found that the prior application of R848 increased the infiltration of leukocytes in the skin and that subsequent delivery of WT1 peptides was more likely to induce WT1-specific CTL. Furthermore, sequential immunization with IL-based formulations was applicable to different types of peptides and cancer models without induction of skin irritation. IL-based transcutaneous delivery of cancer antigen-derived peptides and adjuvants, either alone or together, could be a novel approach to needle-free cancer therapeutic vaccines.

Emerging adjuvants for intradermal vaccination

The majority of vaccines have been delivered into the muscular tissue. Skin contains large amounts of antigen-presenting cells and has been recognized as a more immunogenic site for vaccine delivery. Intradermal delivery has been approved to improve influenza vaccine efficacy and spare influenza vaccine doses. In response to the recent monkeypox outbreak, intradermal delivery has been also approved to stretch the limited monkeypox vaccine doses to immunize more people at risk. Incorporation of vaccine adjuvants is promising to further increase intradermal vaccine efficacy and spare more vaccine doses. Yet, intradermal vaccination is associated with more significant local reactions than intramuscular vaccination. Thus, adjuvants suitable to boost intradermal vaccination need to have a good local safety without inducing overt local reactions. This review introduces currently approved adjuvants in licensed human vaccines and their relative reactogenicity for intradermal delivery and then introduces emerging chemical and physical adjuvants with a good local safety to boost intradermal vaccination. The rational to develop physical adjuvants, the types of physical adjuvants, and the unique advantages of physical adjuvants to boost intradermal vaccination are also introduced in this review.

Adjuvant effect of dendritic cells activator Imiquimod in genetic immunization with HIV-1 p55 Gag

Dendritic cells (DC) are important antigen-presenting cells that have abilities to induce and maintain T-cell immunity, or attenuate it during hyperimmunization. Additional activation of DCs may be useful for vaccination purposes. Imiquimod is known to be a specific agonist of the Toll-like receptors (TLR7), which are located mainly on DCs. To study the effect of DC stimulation on the effectiveness of an HIV-1 p55 gag DNA vaccine in a mice model, we employed 25, 50, and 100 nM of Imiquimod as an adjuvant. Subsequently, Western blot analysis was used to quantify p55 protein production after the immunization. To characterize T-cells immune response, both the frequency of IFN-γ -secreting cells and IFN-γ and IL-4 production were measured, via an ELIspot assay and ELISA, respectively. Low concentrations of Imiquimod were found to effectively stimulate Gag production and the magnitude of the T-cell immune response, whereas higher concentrations reduced vaccination effects. Our results show that the adjuvant effects of Imiquimod depend on concentration. The use of Imiquimod may be helpful to study DC to T cell communication, including possible induction of immunotolerance.

Effective adjuvantation of nanograms of influenza vaccine and induction of cross-protective immunity by physical radiofrequency adjuvant

Novel adjuvants are highly demanded to aid in development of improved or new vaccines against existing or emerging infectious diseases. Considering commonly used Alum and MF59 adjuvants induce tissue stress and release of endogenous danger signals to mediate their adjuvant effects, physical modalities may be used to induce tissue stress and endogenous danger signal release to enhance vaccine-induced immune responses. Furthermore, physical adjuvants are less likely to induce significant systemic adverse reactions due to their localized effects. Recently we found non-invasive radiofrequency (RF) pretreatment of the skin could significantly enhance intradermal vaccine-induced immune responses in murine models that included pandemic influenza vaccine, pre-pandemic vaccine, and influenza internal antigen vaccine. It remained to be explored whether the physical RF adjuvant (RFA) could be used to boost seasonal influenza vaccination, spare vaccine doses, and induce cross-protective immunity. This study found the physical RFA could significantly enhance seasonal influenza vaccine-induced immune responses against each viral strain and robustly enhance low-dose (nanograms) H3N2 vaccine-induced immune responses and protection in murine models. RFA also induced cross-protective immunity against heterologous and heterosubtypic influenza viruses. Further studies found heat shock protein 70 (inducible endogenous danger signal) and myeloid differentiation primary response 88 adaptor played a crucial role in dose-sparing effects of RFA. These data strongly support further development of the physical RFA to boost influenza vaccination.

Combinatorial Herpes Simplex Vaccine Strategies: From Bedside to Bench and Back

The development of vaccines against herpes simplex virus type 1 and type 2 (HSV1 and HSV-2) is an important goal for global health. In this review we reexamined (i) the status of ocular herpes vaccines in clinical trials; and (ii) discusses the recent scientific advances in the understanding of differential immune response between HSV infected asymptomatic and symptomatic individuals that form the basis for the new combinatorial vaccine strategies targeting HSV; and (iii) shed light on our novel "asymptomatic" herpes approach based on protective immune mechanisms in seropositive asymptomatic individuals who are "naturally" protected from recurrent herpetic diseases. We previously reported that phenotypically and functionally distinct HSV-specific memory CD8+ T cell subsets in asymptomatic and symptomatic HSV-infected individuals. Moreover, a better protection induced following a prime/pull vaccine approach that consists of first priming anti-viral effector memory T cells systemically and then pulling them to the sites of virus reactivation (e.g., sensory ganglia) and replication (e.g., eyes and vaginal mucosa), following mucosal administration of vectors expressing T cell-attracting chemokines. In addition, we reported that a combination of prime/pull vaccine approach with approaches to reverse T cell exhaustion led to even better protection against herpes infection and disease. Blocking PD-1, LAG-3, TIGIT and/or TIM-3 immune checkpoint pathways helped in restoring the function of antiviral HSV-specific CD8+ T cells in latently infected ganglia and increased efficacy and longevity of the prime/pull herpes vaccine. We discussed that a prime/pull vaccine strategy that use of asymptomatic epitopes, combined with immune checkpoint blockade would prove to be a successful herpes vaccine approach.

Laser Immunotherapy: A Potential Treatment Modality for Keratinocyte Carcinoma

Simple Summary

In light of expanding incidences of keratinocyte carcinoma (KC) with many patients developing multiple tumors, the demand for new treatment modalities is high. With the approval of cemplimab for locally advanced and metastasizing basal cell carcinoma and squamous cell carcinoma, KC is now included as an indication for systemic immunotherapy. At present, however, systemic KC therapy remains limited by the severe side effects associated with treatment. Immunotherapy might be more broadly applied if locally administered. Localized to the skin, KCs are easily accessible to topical drugs and physical interventions such as laser. There is an increasing appreciation of lasers’ potential to activate an immune response. Further enhancement of the laser-based immune activation might be obtained by combining laser and immunotherapeutic agents, known as laser immunotherapy. In search of new treatment modalities for KC and aiming to broaden the field of KC immunotherapy, this review discusses the current literature on immune activation following both laser monotherapy and laser immunotherapy.

Abstract

The role of the immune system in cancer growth is well recognized and the development of immunotherapy represents a breakthrough in cancer treatment. Recently, the use of systemic immunotherapy was extended to keratinocyte carcinoma (KC), specifically locally advanced and metastasizing basal and squamous cell carcinoma. However, since most KC lesions are non-aggressive, systemic treatment with associated side effects is rarely justified. Conversely, topical immunotherapy with imiquimod remains restricted to premalignant and superficial lesions. Use of laser in the treatment of KC has evolved from physical tumor destruction and laser-assisted drug delivery to laser-mediated immune modulation. Evidence indicates that laser monotherapy can lead to immune cell infiltration, tumor reduction and resistance to tumor re-inoculation. Combining laser with immunotherapeutic agents, termed laser immunotherapy (LIT), may further potentiate immune activation and tumor response. Studies on LIT show not only direct anti-tumor effects but systemic adaptive immunity, illustrated by the prevention of tumor recurrence and regression in distant untreated tumors. These findings imply a therapeutic potential for both local and metastatic disease. This work provides rationales for immune-based treatment of KC and presents the current status of KC immunotherapy. Aiming to expand the field of KC immunotherapy, the review discusses the literature on immune activation following laser monotherapy and LIT.

Brief exposure of skin to near-infrared laser augments early vaccine responses

Rapid establishment of herd immunity with vaccination is effective to combat emerging infectious diseases. Although the incorporation of adjuvant and intradermal (ID) injection could augment early responses to the vaccine, the current chemical or biological adjuvants are inappropriate for this purpose with their side effects and high reactogenicity in the skin. Recently, a near-infrared (NIR) laser has been shown to augment the immune response to ID vaccination and could be alternatively used for mass vaccination programs. Here, we determined the effect of NIR laser as well as licensed chemical adjuvants on the immunogenicity 1, 2, and 4 weeks after ID influenza vaccination in mice. The NIR laser adjuvant augmented early antibody responses, while the widely used alum adjuvant induced significantly delayed responses. In addition, the oil-in-water and alum adjuvants, but not the NIR laser, elicited escalated T_H2 responses with allergenic immunoglobulin E (IgE) responses. The effect of the NIR laser was significantly suppressed in the basic leucine zipper transcription factor ATF-like 3 (Batf3) knockout mice, suggesting a critical role of the cluster of differentiation 103⁺ (CD103)⁺ dendritic cells. The current preliminary study suggests that NIR laser adjuvant is an alternative strategy to chemical and biological agents to timely combat emerging infectious diseases. Moreover, its immunomodulatory property could be used to enhance the efficacy of immunotherapy for allergy and cancer.

Adjuvantation of Influenza Vaccines to Induce Cross-Protective Immunity

Influenza poses a huge threat to global public health. Influenza vaccines are the most effective and cost-effective means to control influenza. Current influenza vaccines mainly induce neutralizing antibodies against highly variable globular head of hemagglutinin and lack cross-protection. Vaccine adjuvants have been approved to enhance seasonal influenza vaccine efficacy in the elderly and spare influenza vaccine doses. Clinical studies found that MF59 and AS03-adjuvanted influenza vaccines could induce cross-protective immunity against non-vaccine viral strains. In addition to MF59 and AS03 adjuvants, experimental adjuvants, such as Toll-like receptor agonists, saponin-based adjuvants, cholera toxin and heat-labile enterotoxin-based mucosal adjuvants, and physical adjuvants, are also able to broaden influenza vaccine-induced immune responses against non-vaccine strains. This review focuses on introducing the various types of adjuvants capable of assisting current influenza vaccines to induce cross-protective immunity in preclinical and clinical studies. Mechanisms of licensed MF59 and AS03 adjuvants to induce cross-protective immunity are also introduced. Vaccine adjuvants hold a great promise to adjuvant influenza vaccines to induce cross-protective immunity.

Laser adjuvant for vaccination

The use of an immunologic adjuvant to augment the immune response is essential for modern vaccines which are relatively ineffective on their own. In the past decade, researchers have been consistently reporting that skin treatment with a physical parameter, namely laser light, augments the immune response to vaccine and functions as an immunologic adjuvant. This "laser adjuvant" has numerous advantages over the conventional chemical or biological agents; it is free from cold chain storage, hypodermic needles, biohazardous sharp waste, irreversible formulation with vaccine antigen, undesirable biodistribution in vital organs, or unknown long-term toxicity. Since vaccine formulations are given to healthy populations, these characteristics render the "laser adjuvant" significant advantages for clinical use and open a new developmental path for a safe and effective vaccine. In addition, laser technology has been used in the clinic for more than three decades and is therefore technically matured and has been proved to be safe. Currently, four classes of laser adjuvant have been reported; ultrashort pulsed, non-pulsed, non-ablative fractional, and ablative fractional lasers. Since each class of the laser adjuvant shows a distinct mechanism of action, a proper choice is necessary to craft an effective vaccine formulation toward a desired clinical benefit for a clinical vaccine to maximize protection. In addition, data also suggest that further improvement in the efficacy is possible when a laser adjuvant is combined with chemical or biological adjuvant(s). To realize these goals, further efforts to uncover the molecular mechanisms of action of the laser adjuvants is warranted. This review provides a summary and comments of the recent updates in the laser adjuvant technology.

Mucosal Immunization with a pH-Responsive Nanoparticle Vaccine Induces Protective CD8+ Lung-Resident Memory T Cells

Tissue-resident memory T cells (T_RM) patrol nonlymphoid organs and provide superior protection against pathogens that commonly infect mucosal and barrier tissues, such as the lungs, intestine, liver, and skin. Thus, there is a need for vaccine technologies that can induce a robust, protective T_RM response in these tissues. Nanoparticle (NP) vaccines offer important advantages over conventional vaccines; however, there has been minimal investigation into the design of NP-based vaccines for eliciting T_RM responses. Here, we describe a pH-responsive polymeric nanoparticle vaccine for generating antigen-specific CD8⁺ T_RM cells in the lungs. With a single intranasal dose, the NP vaccine elicited airway- and lung-resident CD8⁺ T_RM cells and protected against respiratory virus challenge in both sublethal (vaccinia) and lethal (influenza) infection models for up to 9 weeks after immunization. In elucidating the contribution of material properties to the resulting T_RM response, we found that the pH-responsive activity of the carrier was important, as a structurally analogous non-pH-responsive control carrier elicited significantly fewer lung-resident CD8⁺ T cells. We also demonstrated that dual-delivery of protein antigen and nucleic acid adjuvant on the same NP substantially enhanced the magnitude, functionality, and longevity of the antigen-specific CD8⁺ T_RM response in the lungs. Compared to administration of soluble antigen and adjuvant, the NP also mediated retention of vaccine cargo in pulmonary antigen-presenting cells (APCs), enhanced APC activation, and increased production of T_RM-related cytokines. Overall, these data suggest a promising vaccine platform technology for rapid generation of protective CD8⁺ T_RM cells in the lungs.

Blockade of PD-1 and LAG-3 Immune Checkpoints Combined with Vaccination Restores the Function of Antiviral Tissue-Resident CD8+ TRM Cells and Reduces Ocular Herpes Simplex Infection and Disease in HLA Transgenic Rabbits

Chronic viruses such as herpes simplex virus 1 (HSV-1) evade the hosts' immune system by inducing the exhaustion of antiviral T cells. In the present study, we found that exhausted HSV-specific CD8⁺ T cells, with elevated expression of programmed death ligand-1 (PD-1) and lymphocyte activation gene-3 (LAG-3) receptors were frequent in symptomatic patients, with a history of numerous episodes of recurrent corneal herpetic disease, compared to asymptomatic patients who never had corneal herpetic disease. Subsequently, using a rabbit model of recurrent ocular herpes, we found that the combined blockade of PD-1 and LAG-3 pathways with antagonist antibodies significantly restored the function of tissue-resident antiviral CD8⁺ T_RM cells in both the cornea and the trigeminal ganglia (TG). An increased number of functional tissue-resident HSV-specific CD8⁺ T_RM cells in latently infected rabbits was associated with protection against recurrent herpes infection and disease. Compared to the PD-1 or LAG-3 blockade alone, the combined blockade of PD-1 and LAG-3 appeared to have a synergistic effect in generating frequent polyfunctional Ki-67⁺, IFN-γ⁺, CD107⁺, and CD8⁺ T cells. Moreover, using the human leukocyte antigen (HLA) transgenic rabbit model, we found that dual blockade of PD-1 and LAG-3 reinforced the effect of a multiepitope vaccine in boosting the frequency of HSV-1-specific CD8⁺ T_RM cells and reducing disease severity. Thus, both the PD-1 and the LAG-3 exhaustion pathways play a fundamental role in ocular herpes T cell immunopathology and provide important immune checkpoint targets to combat ocular herpes.IMPORTANCE HSV-specific tissue-resident memory CD8⁺ T_RM cells play a critical role in preventing virus reactivation from latently infected TG and subsequent virus shedding in tears that trigger the recurrent corneal herpetic disease. In this report, we determined how the dual blockade of PD-1 and LAG-3 immune checkpoints, combined with vaccination, improved the function of CD8⁺ T_RM cells associated with a significant reduction in recurrent ocular herpes in HLA transgenic (Tg) rabbit model. The combined blockade of PD-1 and LAG-3 appeared to have a synergistic effect in generating frequent polyfunctional CD8⁺ T_RM cells that infiltrated both the cornea and the TG. The preclinical findings using the established HLA Tg rabbit model of recurrent herpes highlight that blocking immune checkpoints combined with a T cell-based vaccine would provide an important strategy to combat recurrent ocular herpes in the clinic.

Therapeutic Mucosal Vaccination of Herpes Simplex Virus 2-Infected Guinea Pigs with Ribonucleotide Reductase 2 (RR2) Protein Boosts Antiviral Neutralizing Antibodies and Local Tissue-Resident CD4+ and CD8+ TRM Cells Associated with Protection against Recurrent Genital Herpes

Reactivation of herpes simplex virus 2 (HSV-2) from latency causes viral shedding that develops into recurrent genital lesions. The immune mechanisms of protection against recurrent genital herpes remain to be fully elucidated. In this preclinical study, we investigated the protective therapeutic efficacy, in the guinea pig model of recurrent genital herpes, of subunit vaccine candidates that were based on eight recombinantly expressed HSV-2 envelope and tegument proteins. These viral protein antigens (Ags) were rationally selected for their ability to recall strong CD4+ and CD8+ T-cell responses from naturally "protected" asymptomatic individuals, who, despite being infected, never develop any recurrent herpetic disease. Out of the eight HSV-2 proteins, the envelope glycoprotein D (gD), the tegument protein VP22 (encoded by the UL49 gene), and ribonucleotide reductase subunit 2 protein (RR2; encoded by the UL40 gene) produced significant protection against recurrent genital herpes. The RR2 protein, delivered either intramuscularly or intravaginally with CpG and alum adjuvants, (i) boosted the highest neutralizing antibodies, which appear to cross-react with both gB and gD, and (ii) enhanced the numbers of functional gamma interferon (IFN-γ)-producing CRTAM+ CFSE+ CD4+ and CRTAM+ CFSE+ CD8+ TRM cells, which express low levels of PD-1 and TIM-3 exhaustion markers and were localized to healed sites of the vaginal mucocutaneous (VM) tissues. The strong B- and T-cell immunogenicity of the RR2 protein was associated with a significant decrease in virus shedding and a reduction in both the severity and frequency of recurrent genital herpes lesions. In vivo depletion of either CD4+ or CD8+ T cells significantly abrogated the protection. Taken together, these preclinical results provide new insights into the immune mechanisms of protection against recurrent genital herpes and promote the tegument RR2 protein as a viable candidate Ag to be incorporated in future genital herpes therapeutic mucosal vaccines.IMPORTANCE Recurrent genital herpes is one of the most common sexually transmitted diseases, with a global prevalence of HSV-2 infection predicted to be over 536 million worldwide. Despite the availability of many intervention strategies, such as sexual behavior education, barrier methods, and the costly antiviral drug treatments, eliminating or at least reducing recurrent genital herpes remains a challenge. Currently, no FDA-approved therapeutic vaccines are available. In this preclinical study, we investigated the immunogenicity and protective efficacy, in the guinea pig model of recurrent genital herpes, of subunit vaccine candidates that were based on eight recombinantly expressed herpes envelope and tegument proteins. We discovered that similar to the dl5-29 vaccine, based on a replication-defective HSV-2 mutant virus, which has been recently tested in clinical trials, the RR2 protein-based subunit vaccine elicited a significant reduction in virus shedding and a decrease in both the severity and frequency of recurrent genital herpes sores. This protection correlated with an increase in numbers of functional tissue-resident IFN-γ+ CRTAM+ CFSE+ CD4+ and IFN-γ+ CRTAM+ CFSE+ CD8+ TRM cells that infiltrate healed sites of the vaginal tissues. Our study sheds new light on the role of TRM cells in protection against recurrent genital herpes and promotes the RR2-based subunit therapeutic vaccine to be tested in the clinic.

Vaccine-induced antibodies target sequestered viral antigens to prevent ocular HSV-1 pathogenesis, preserve vision, and preempt productive neuronal infection

The cornea is essential for vision yet highly sensitive to immune-mediated damage following infection. Generating vaccines that provide sterile immunity against ocular surface pathogens without evoking vision loss is therefore clinically challenging. Here, we tested a prophylactic live-attenuated vaccine against herpes simplex virus type 1 (HSV-1), a widespread human pathogen that can cause corneal blindness. Parenteral vaccination of mice resulted in sterile immunity to subsequent HSV-1 challenge in the cornea and suppressed productive infection of the nervous system. This protection was unmatched by a relevant glycoprotein subunit vaccine. Efficacy of the live-attenuated vaccine involved a T-dependent humoral immune response and complement C3 but not Fcγ-receptor 3 or interferon-α/β signaling. Proteomic analysis of viral proteins recognized by antiserum revealed an unexpected repertoire dominated by sequestered antigens rather than surface-exposed envelope glycoproteins. Ocular HSV-1 challenge in naive and subunit-vaccinated mice triggered vision loss and severe ocular pathologies including corneal opacification, scar formation, neovascularization, and sensation loss. However, corneal pathology was absent in mice receiving the live-attenuated vaccine concomitant with complete preservation of visual acuity. Collectively, this is the first comprehensive report of a prophylactic vaccine candidate that elicits resistance to ocular HSV-1 infection while fully preserving the cornea and visual acuity.

Topical Application of a Vitamin A Derivative and Its Combination With Non-ablative Fractional Laser Potentiates Cutaneous Influenza Vaccination

Skin contains a large number of antigen presenting cells, making intradermal (ID) injection one of the most effective ways for vaccine administration. However, although current adjuvants may cause severe local reactions and inflammations in the skin, no adjuvant has been approved for ID vaccination so far. Here, we report that topical application of all-trans retinoic acid (ATRA), a vitamin A derivative produced in the human body, augmented cutaneous influenza vaccination. The adjuvant effects were evaluated in a murine vaccination/challenge model by using A/California/07/2009 pandemic vaccine (09V) or a seasonal influenza vaccine (SIV). ATRA drove a Th2-biased immune response, as demonstrated by profoundly elevated IgG1 titer rather than IgG2 titer. Combining ATRA with a non-ablative fractional laser (NAFL), which represents a new category of vaccine adjuvant utilizing physical stimuli to induce self-immune stimulators, further enhanced the efficacy of influenza vaccines with a more balanced Th1/Th2 immune response. The dual adjuvant strengthened cross-reactive immune responses against both homogenous and heterogeneous influenza viral strains. Analysis of gene expression profile showed that ATRA/NAFL stimulated upregulation of cytosolic nucleic acid sensors and their downstream factors, leading to a synergistic elevation of type I interferon expression. Consistent with this finding, knocking out IRF3 or IRF7, two key downstream regulatory factors in most nucleic acid sensing pathways, resulted in a significant decrease in the adjuvant effect of ATRA/NAFL. Thus, our study demonstrates that the self molecule ATRA could boost cutaneous influenza vaccination either alone or ideally in combination with NAFL.

Augmentation of vaccine-induced humoral and cellular immunity by a physical radiofrequency adjuvant

Protein/subunit vaccines often require external adjuvants to induce protective immunity. Due to the safety concern of chemical adjuvants, physical adjuvants were recently explored to boost vaccination. Physical adjuvants use physical energies rather than chemicals to stimulate tissue stress and endogenous danger signal release to boost vaccination. Here we present the safety and potency of non-invasive radiofrequency treatment to boost intradermal vaccination in murine models. We show non-invasive radiofrequency can increase protein antigen-induced humoral and cellular immune responses with adjuvant effects comparable to widely used chemical adjuvants. Radiofrequency adjuvant can also safely boost pandemic 2009 H1N1 influenza vaccination with adjuvant effects comparable to MF59-like AddaVax adjuvant. We find radiofrequency adjuvant induces heat shock protein 70 (HSP70) release and activates MyD88 to mediate the adjuvant effects. Physical radiofrequency can potentially be a safe and potent adjuvant to augment protein/subunit vaccine-induced humoral and cellular immune responses.

Tumor Resident Memory T Cells: New Players in Immune Surveillance and Therapy

Tissue resident memory T cells (Trm) are a subset of memory T cells mainly described in inflammation and infection settings. Their location in peripheral tissues, such as lungs, gut, or skin, makes them the earliest T cell population to respond upon antigen recognition or under inflammatory conditions. The study of Trm cells in the field of cancer, and particularly in cancer immunotherapy, has recently gained considerable momentum. Different reports have shown that the vaccination route is critical to promote Trm generation in preclinical cancer models. Cancer vaccines administered directly at the mucosa, frequently result in enhanced Trm formation in mucosal cancers compared to vaccinations via intramuscular or subcutaneous routes. Moreover, the intratumoral presence of T cells expressing the integrin CD103 has been reported to strongly correlate with a favorable prognosis for cancer patients. In spite of recent progress, the full spectrum of Trm anti-tumoral functions still needs to be fully established, particularly in cancer patients, in different clinical contexts. In this mini-review we focus on the recent vaccination strategies aimed at generating Trm cells, as well as evidence supporting their association with patient survival in different cancer types. We believe that collectively, this information provides a strong rationale to target Trm for cancer immunotherapy.

A Systematic Review: The Role of Resident Memory T Cells in Infectious Diseases and Their Relevance for Vaccine Development

Background

Resident memory T cells have emerged as key players in the immune response generated against a number of pathogens. Their ability to take residence in non-lymphoid peripheral tissues allows for the rapid deployment of secondary effector responses at the site of pathogen entry. This ability to provide enhanced regional immunity has gathered much attention, with the generation of resident memory T cells being the goal of many novel vaccines.

Objectives

This review aimed to systematically analyze published literature investigating the role of resident memory T cells in human infectious diseases. Known effector responses mounted by these cells are summarized and key strategies that are potentially influential in the rational design of resident memory T cell inducing vaccines have also been highlighted.

Methods

A Boolean search was applied to Medline, SCOPUS, and Web of Science. Studies that investigated the effector response generated by resident memory T cells and/or evaluated strategies for inducing these cells were included irrespective of published date. Studies must have utilized an established technique for identifying resident memory T cells such as T cell phenotyping.

Results

While over 600 publications were revealed by the search, 147 articles were eligible for inclusion. The reference lists of included articles were also screened for other eligible publications. This resulted in the inclusion of publications that studied resident memory T cells in the context of over 25 human pathogens. The vast majority of studies were conducted in mouse models and demonstrated that resident memory T cells mount protective immune responses.

Conclusion

Although the role resident memory T cells play in providing immunity varies depending on the pathogen and anatomical location they resided in, the evidence overall suggests that these cells are vital for the timely and optimal protection against a number of infectious diseases. The induction of resident memory T cells should be further investigated and seriously considered when designing new vaccines.