Protective CD4+ Th1 cell-mediated immunity is reliant upon execution of effector function prior to the establishment of the pathogen niche

The Immune Memory Response of In Vitro-Polarised Th1, Th2, and Th17 Cells in the Face of Ovalbumin-Transgenic Leishmania major in a Mouse Model

Th1 and Th2 cytokines determine the outcome of Leishmania major infection and immune protection depends mainly on memory T cells induced during vaccination. This largely hinges on the nature and type of memory T cells produced. In this study, transgenic Leishmania major strains expressing membrane-associated ovalbumin (mOVA) and soluble ovalbumin (sOVA) were used as a model to study whether fully differentiated Th1/Th2 and Th17 cells can recall immune memory and tolerate pathogen manipulation. Naïve OT-II T cells were polarised in vitro into Th1/Th2 cells, and these cells were transferred adoptively into recipient mice. Following the transferral of the memory cells, the recipient mice were challenged with OVA transgenic Leishmania major and a wild-type parasite was used a control. The in vitro-polarised T helper cells continued to produce the same cytokine signatures after being challenged by both forms of OVA-expressing Leishmania major parasites in vivo. This suggests that antigen-experienced cells remain the same or unaltered in the face of OVA-transgenic Leishmania major. Such ability of these antigen-experienced cells to remain resilient to manipulation by the parasite signifies that vaccines might be able to produce immune memory responses and defend against parasitic immune manipulation in order to protect the host from infection.

Live attenuated-nonpathogenic Leishmania and DNA structures as promising vaccine platforms against leishmaniasis: innovations can make waves

Leishmaniasis is a vector-borne disease caused by the protozoan parasite of Leishmania genus and is a complex disease affecting mostly tropical regions of the world. Unfortunately, despite the extensive effort made, there is no vaccine available for human use. Undoubtedly, a comprehensive understanding of the host-vector-parasite interaction is substantial for developing an effective prophylactic vaccine. Recently the role of sandfly saliva on disease progression has been uncovered which can make a substantial contribution in vaccine design. In this review we try to focus on the strategies that most probably meet the prerequisites of vaccine development (based on the current understandings) including live attenuated/non-pathogenic and subunit DNA vaccines. Innovative approaches such as reverse genetics, CRISP/R-Cas9 and antibiotic-free selection are now available to promisingly compensate for intrinsic drawbacks associated with these platforms. Our main goal is to call more attention toward the prerequisites of effective vaccine development while controlling the disease outspread is a substantial need.

Memory T cells: promising biomarkers for evaluating protection and vaccine efficacy against leishmaniasis

Understanding the immune response to Leishmania infection and identifying biomarkers that correlate with protection are crucial for developing effective vaccines. One intriguing aspect of Leishmania infection is the persistence of parasites, even after apparent lesion healing. Various host cells, including dendritic cells, fibroblasts, and Langerhans cells, may serve as safe sites for latent infection. Memory T cells, especially tissue-resident memory T cells (TRM), play a crucial role in concomitant immunity against cutaneous Leishmania infections. These TRM cells are long-lasting and can protect against reinfection in the absence of persistent parasites. CD4+ TRM cells, in particular, have been implicated in protection against Leishmania infections. These cells are characterized by their ability to reside in the skin and rapidly respond to secondary infections by producing cytokines such as IFN-γ, which activates macrophages to kill parasites. The induction of CD4+ TRM cells has shown promise in experimental immunization, leading to protection against Leishmania challenge infections. Identifying biomarkers of protection is a critical step in vaccine development and CD4+ TRM cells hold potential as biomarkers, as their presence and functions may correlate with protection. While recent studies have shown that Leishmania-specific memory CD4+ T-cell subsets are present in individuals with a history of cutaneous leishmaniasis, further studies are needed to characterize CD4+ TRM cell populations. Overall, this review highlights the importance of memory T cells, particularly skin-resident CD4+ TRM cells, as promising targets for developing effective vaccines against leishmaniasis and as biomarkers of immune protection to assess the efficacy of candidate vaccines against human leishmaniasis.

In vitro and in vivo evaluation of immune response of poly(lactic acid) nanoparticles with different end groups

Poly(lactic acid) (PLA) has excellent properties of biodegradability and biocompatibility, which is a US Food and Drug Administration (FDA) approved biopolymer for the preparation of safe and effective vaccines, drugs, and gene delivery systems. However, there still exists a great problem whether and how the end group affects the immune response of PLA vaccines. Therefore, the aim of this study was to evaluate the in vitro and in vivo of immune response of PLA nanoparticles (NPs) with carboxyl (COOH) and ester (COOR) end groups. In vitro experiments suggested COOH NPs could promote the higher phagocytosis and activation of bone marrow dendritic cells (BMDCs) with a lower cytotoxicity. In vivo experiments showed that COOR NPs and COOH NPs could strongly elicit IgG, IgG1, and IgG2a responses both in the short and long-terms. However, the highest T cell and B cell activation, and central memory T cells response was induced by COOH NPs. In addition, the COOH NPs could significantly enhance splenocytes proliferation and cytokines secretion. Thus, the PLA with the COOH end group shows greater potential as efficient carrier materials of NPs for enhancing cellular and humoral immune responses.

Clinical and immunological spectra of human cutaneous leishmaniasis in North Africa and French Guiana

Cutaneous leishmaniasis (CL) caused by infection with the parasite Leishmania exhibits a large spectrum of clinical manifestations ranging from single healing to severe chronic lesions with the manifestation of resistance or not to treatment. Depending on the specie and multiple environmental parameters, the evolution of lesions is determined by a complex interaction between parasite factors and the early immune responses triggered, including innate and adaptive mechanisms. Moreover, lesion resolution requires parasite control as well as modulation of the pathologic local inflammation responses and the initiation of wound healing responses. Here, we have summarized recent advances in understanding the in situ immune response to cutaneous leishmaniasis: i) in North Africa caused by Leishmania (L.) major, L. tropica, and L. infantum, which caused in most cases localized autoresolutives forms, and ii) in French Guiana resulting from L. guyanensis and L. braziliensis, two of the most prevalent strains that may induce potentially mucosal forms of the disease. This review will allow a better understanding of local immune parameters, including cellular and cytokines release in the lesion, that controls infection and/or protect against the pathogenesis in new world compared to old world CL.

Deletion of MIF gene from live attenuated LdCen-/- parasites enhances protective CD4+ T cell immunity

Vaccination with live attenuated Leishmania parasites such as centrin deleted Leishmania donovani (LdCen^-/-) against visceral leishmaniasis has been reported extensively. The protection induced by LdCen^-/- parasites was mediated by both CD4⁺ and CD8⁺ T cells. While the host immune mediators of protection are known, parasite determinants that affect the CD4⁺ and CD8⁺ T cell populations remain unknown. Parasite encoded inflammatory cytokine MIF has been shown to modulate the T cell differentiation characteristics by altering the inflammation induced apoptosis during contraction phase in experimental infections with Leishmania or Plasmodium. Neutralization of parasite encoded MIF either by antibodies or gene deletion conferred protection in Plasmodium and Leishmania studies. We investigated if the immunogenicity and protection induced by LdCen^-/- parasites is affected by deleting MIF genes from this vaccine strain. Our results showed that LdCen^-/-MIF^-/- immunized group presented higher percentage of CD4⁺ and CD8⁺ central memory T cells, increased CD8⁺ T cell proliferation after challenge compared to LdCen^-/- immunization. LdCen^-/-MIF^-/- immunized group presented elevated production of IFN-γ⁺ and TNF-α⁺ CD4⁺ T cells concomitant with a reduced parasite load in spleen and liver compared to LdCen^-/-group following challenge with L. infantum. Our results demonstrate the role of parasite induced factors involved in protection and long-term immunity of vaccines against VL.

Novel approaches to preventing phagosomal infections: timing is key

Prophylactic vaccination strategies designed to prevent diseases caused by pathogens using the phagolysosome of innate immune cells as a site of intracellular replication and survival have been largely ineffective. These include Mycobacterium tuberculosis (Mtb), Leishmania spp., and Cryptococcus spp. These failed strategies have traditionally targeted CD4⁺ T helper (Th) 1 cell-mediated immune memory, deeming it crucial for vaccine efficacy. This failure warrants an investigation of alternative mediators of protection. Here, we suggest three novel approaches to activate phagocytic cells prior to or at the time of infection. We hypothesize that preventing the formation of the pathogen niche within the phagolysosome is essential for preventing disease, and a greater emphasis on the timing of phagocyte activation should generate more effective prophylactic treatment options.

Leishmania Major Centrin Gene-Deleted Parasites Generate Skin Resident Memory T-Cell Immune Response Analogous to Leishmanization

Leishmaniasis is a vector-borne parasitic disease transmitted through the bite of a sand fly with no available vaccine for humans. Recently, we have developed a live attenuated Leishmania major centrin gene-deleted parasite strain (LmCen^-/- ) that induced protection against homologous and heterologous challenges. We demonstrated that the protection is mediated by IFN (Interferon) γ-secreting CD4⁺ T-effector cells and multifunctional T cells, which is analogous to leishmanization. In addition, in a leishmanization model, skin tissue-resident memory T (TRM) cells were also shown to be crucial for host protection. In this study, we evaluated the generation and function of skin TRM cells following immunization with LmCen^-/- parasites and compared those with leishmanization. We show that immunization with LmCen^-/- generated skin CD4+ TRM cells and is supported by the induction of cytokines and chemokines essential for their production and survival similar to leishmanization. Following challenge with wild-type L. major, TRM cells specific to L. major were rapidly recruited and proliferated at the site of infection in the immunized mice. Furthermore, upon challenge, CD4⁺ TRM cells induce higher levels of IFNγ and Granzyme B in the immunized and leishmanized mice than in non-immunized mice. Taken together, our studies demonstrate that the genetically modified live attenuated LmCen ^-/- vaccine generates functional CD4⁺ skin TRM cells, similar to leishmanization, that may play a crucial role in host protection along with effector T cells as shown in our previous study.