A TCR transgenic mouse reactive with multiple systemic dimorphic fungi

Dimorphic fungi collectively account for 5-10 million new infections annually worldwide. Ongoing efforts seek to clarify mechanisms of cellular resistance to these agents and develop vaccines. A major limitation in studying the development of protective T cells in this group of organisms is the lack of tools to detect, enumerate, and characterize fungus-specific T cells during vaccination and infection. We generated a TCR transgenic mouse (Bd 1807) whose CD4(+) T cells respond to a native epitope in Blastomyces dermatitidis and also in Histoplasma capsulatum. In this study, we characterize the mouse, reveal its applications, and extend our analysis showing that 1807 cells also respond to the related dimorphic fungi Coccidioides posadasii and Paracoccidioides lutzii. On adoptive transfer into vaccinated wild-type mice, 1807 cells become activated, proliferate, and expand in the draining lymph nodes, and they differentiate into T1 effectors after trafficking to the lung upon lethal experimental challenge. Bd 1807 cells confer vaccine-induced resistance against B. dermatitidis, H. capsulatum, and C. posadasii. Transfer of naive 1807 cells at serial intervals postvaccination uncovered the prolonged duration of fungal Ag presentation. Using 1807 cells, we also found that the administration of vaccine only once induced a maximal pool of effector/memory CD4(+) cells and protective immunity by 4 wk after vaccination. The autologous adoptive transfer system described in this study reveals novel features of antifungal immunity and offers a powerful approach to study the differentiation of Ag-specific T cells responsive to multiple dimorphic fungi and the development of CD4(+) T cell memory needed to protect against fungal infection.

V beta1+ J beta1.1+/V alpha2+ J alpha49+ CD4+ T cells mediate resistance against infection with Blastomyces dermatitidis

Immunization with a cell wall/membrane (CW/M) and yeast cytosol extract (YCE) crude antigen from Blastomyces dermatitidis confers T-cell-mediated resistance against lethal experimental infection in mice. We isolated and characterized T cells that recognize components of these protective antigens and mediate protection. CD4+ T-cell clones elicited with CW/M antigen adoptively transferred protective immunity when they expressed a V alpha2+ J alpha49+/V beta1+ J beta1.1+ heterodimeric T-cell receptor (TCR) and produced high levels of gamma interferon (IFN-gamma). In contrast, V beta8.1/8.2+ CD4+ T-cell clones that were reactive against CW/M and YCE antigens and produced little or no IFN-gamma either failed to mediate protection or exacerbated the infection depending on the level of interleukin-5 expression. Thus, the outgrowth of protective T-cell clones against immunodominant antigens of B. dermatitidis is biased by a combination of the TCR repertoire and Th1 cytokine production.

Analysis of non-adhesive pathogenic mechanisms of BAD1 on Blastomyces dermatitidis

The adhesin BAD1 is required for virulence of Blastomyces dermatitidis in a pulmonary model of infection. Herein, we explored mechanisms by which BAD1 enhances pathogenicity of the fungus. Isogenic strains with and without BAD1 exhibited similar phenotypic differences in virulence by pulmonary and intravenous routes of infection, indicating that BAD1 may exert virulence beyond adherence to respiratory lining cells. Non-adhesive mechanisms including maintenance of intrinsic resistance of yeast against phagocyte responses and products were excluded. A shift in the balance of type 1 and 2 cytokines and in the cellular profile of the inflammatory response after the first week of pulmonary infection was associated with BAD1. By the second week of infection, infection with wild-type yeast was associated with less IL-12 and IFN-gamma, and more IL-10, and an influx of inflammatory cells rich in neutrophils and poor in T-cells, when compared to infection with the BAD1 null strain. Taken together with previously reported BAD1 perturbations of TNF-gamma and TGF-beta, these data suggest that BAD1 contributes significantly to the pathogenicity of B. dermatitidis by also deviating host adaptive immunity, and leukocyte responses.

Differential requirements of T cell subsets for CD40 costimulation in immunity to Blastomyces dermatitidis

Cell-mediated immunity and production of type 1 cytokines are the main defenses against pathogenic fungi. Ligation of CD40 by CD40L on T cells is critical for the induction of these immune responses in vivo. We explored the role of CD40/CD40L interactions in vaccine immunity to Blastomyces dermatitidis by immunizing CD40(-/-) and CD40L(-/-) mice and analyzing their resistance to reinfection in a murine pulmonary model. In the absence of CD40 or CD40L, CD4(+) cells failed to get primed or produce type 1 cytokine and impaired the generation of CD8(+) T1 cells. The CD8(+) T cell defect was not due to regulatory T cells or impaired APC maturation or Ag presentation to T cells. If CD4(+) cells were first eliminated, vaccination of CD40(-/-) and CD40L(-/-) mice restored priming of CD8(+) cells, type 1 cytokine production, and resistance. Hence, CD4(+) and CD8(+) cells differ sharply in their requirement for CD40/CD40L interaction during the generation of antifungal immunity. Despite the plasticity of T cell subsets in vaccine immunity, in absence of CD40/CD40L interaction, CD4(+) cells may impede the priming of CD8(+) cells at the cost of host survival against a lethal infectious disease.

Vaccine immunity to pathogenic fungi overcomes the requirement for CD4 help in exogenous antigen presentation to CD8+ T cells: implications for vaccine development in immune-deficient hosts

Systemic fungal infections with primary and opportunistic pathogens have become increasingly common and represent a growing health menace in patients with AIDS and other immune deficiencies. T lymphocyte immunity, in particular the CD4+ Th 1 cells, is considered the main defense against these pathogens, and their absence is associated with increased susceptibility. It would seem illogical then to propose vaccinating these vulnerable patients against fungal infections. We report here that CD4+ T cells are dispensable for vaccine-induced resistance against experimental fungal pulmonary infections with two agents, Blastomyces dermatitidis an extracellular pathogen, and Histoplasma capsulatum a facultative intracellular pathogen. In the absence of T helper cells, exogenous fungal antigens activated memory CD8+ cells in a major histocompatibility complex class I-restricted manner and CD8+ T cell-derived cytokines tumor necrosis factor alpha, interferon gamma, and granulocyte/macrophage colony-stimulating factor-mediated durable vaccine immunity. CD8+ T cells could also rely on alternate mechanisms for robust vaccine immunity, in the absence of some of these factors. Our results demonstrate an unexpected plasticity of immunity in compromised hosts at both the cellular and molecular level and point to the feasibility of developing vaccines against invasive fungal infections in patients with severe immune deficiencies, including those with few or no CD4+ T cells.

Requisite elements in vaccine immunity to Blastomyces dermatitidis: plasticity uncovers vaccine potential in immune-deficient hosts

Understanding fundamental mechanisms of vaccine immunity will allow proper use and optimization of vaccines. Vaccination with a genetically engineered, live, attenuated strain of Blastomyces dermatitidis carrying a targeted deletion at the BAD1 locus confers sterilizing immunity against experimental lethal pulmonary infection. We found in this study that alphabeta T cells are requisite for durable vaccine immunity, whereas other T and B cells are dispensable. In immune-competent animals, CD4(+) T-cell derived cytokines TNF-alpha and IFN-gamma mediate vaccine immunity. Surprisingly, these factors are dispensable in immune-deficient animals, which rely on alternate mechanisms for robust vaccine immunity, yet still require O(2)(-) production rather than generation of NO. Our results clarify the cellular and molecular bases behind the first genetically engineered fungal vaccine. They also illustrate a sharp difference in vaccine mechanisms between immune-competent and immune-deficient hosts, which underscores the plasticity of residual immune elements in compromised hosts, and points to the feasibility of developing vaccines against invasive fungal infection in this fast growing patient population.

Mutation of the WI-1 gene yields an attenuated blastomyces dermatitidis strain that induces host resistance

Systemic fungal infections are becoming more common and difficult to treat, and vaccine prevention is not available. Pulmonary infection with the dimorphic fungus Blastomyces dermatitidis often progresses and requires treatment to prevent fatality. We recently created a recombinant strain of the fungus lacking the WI-1 adhesin and pathogenicity. We show here that administration of viable yeast of this attenuated strain vaccinates against lethal pulmonary experimental infection due to isogenic and nonisogenic strains from diverse geographic regions. To our knowledge, this is the first example of a recombinant attenuated vaccine against fungi. The vaccine induces delayed-type hypersensitivity and polarized type 1 cytokine responses, which are linked with resistance. A cell-wall/membrane (CW/M) antigen from the vaccine strain also induces polarized and protective immune responses. Lymph node cells and CD4(+) T-cell lines raised with CW/M antigen transfer protective immunity when they release type 1 cytokine IFN-gamma, but not when they release IL-4, and neutralization of IFN-gamma confirmed its role in vivo. Thus, by mutating a pathogenetic locus in a dimorphic fungus, we have created an attenuated vaccine strain and have begun to elucidate fungal and host elements requisite for vaccine immunity.

Purification and partial sequence analysis of murine B cell growth factor II (interleukin 5)

Murine B cell growth factor II (BCGF-II/interleukin 5) was purified from the conditioned media of the helper T cell line D10 . G4 . 1. The purification scheme consisted of sequential batch adsorption onto trimethylsilyl-controlled pore glass beads, high pressure ion exchange chromatography, and reverse phase high pressure liquid chromatography. The purified BCGF-II had a relative molecular weight of 45,000 when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions. Identical analysis of BCGF-II under reducing conditions yielded a m.w. of 22,500, suggesting that native BCGF-II exists as a homodimer. The NH2-terminal amino acid sequence of the purified lymphokine was determined by automated Edman degradation. A single amino acid sequence of 24 residues was obtained that, upon comparison, was contained within the cDNA pSP6K-mTRF23 recently described as encoding murine BCGF-II/T cell-replacing factor. The NH2-terminal methionine in mature BCGF-II is found at position 21 of the amino acid sequence predicted from the cDNA pSP6K-mTRF23. This finding supports the contention of Kinashi et al. (Kinashi, T., N. Harada, E. Severinson, T. Tanabe, P. Sideras, M. Konishi, C. Azuma, A. Tominaga, S. Bergstedt-Lindqvist, M. Takahashi, F. Matsuda, Y. Yaoita, K. Takatsu, and T. Honjo. 1986. Nature 324:70) that amino acids 1-20 serve as the signal sequence for the BCGF-II gene. The ability of BCGF-II to stimulate the proliferation of the B cell lymphoma BCL1 was used to assess the potency of the lymphokine. BCGF-II at 13.5 pM induced 50% of the maximal proliferative response in the BCL1 cells; concentrations as low as 2 pM were still effective in stimulating the growth of the cells. Assuming that the amount of BCGF-II necessary to mount a 50% response in the BCL1 assay is defined as one unit of activity, then the purified BCGF-II has a specific activity of 16.5 U/ng of protein.

Purification and partial sequence analysis of murine B cell growth factor II (interleukin 5)

Murine B cell growth factor II (BCGF-II/interleukin 5) was purified from the conditioned media of the helper T cell line D10 . G4 . 1. The purification scheme consisted of sequential batch adsorption onto trimethylsilyl-controlled pore glass beads, high pressure ion exchange chromatography, and reverse phase high pressure liquid chromatography. The purified BCGF-II had a relative molecular weight of 45,000 when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions. Identical analysis of BCGF-II under reducing conditions yielded a m.w. of 22,500, suggesting that native BCGF-II exists as a homodimer. The NH2-terminal amino acid sequence of the purified lymphokine was determined by automated Edman degradation. A single amino acid sequence of 24 residues was obtained that, upon comparison, was contained within the cDNA pSP6K-mTRF23 recently described as encoding murine BCGF-II/T cell-replacing factor. The NH2-terminal methionine in mature BCGF-II is found at position 21 of the amino acid sequence predicted from the cDNA pSP6K-mTRF23. This finding supports the contention of Kinashi et al. (Kinashi, T., N. Harada, E. Severinson, T. Tanabe, P. Sideras, M. Konishi, C. Azuma, A. Tominaga, S. Bergstedt-Lindqvist, M. Takahashi, F. Matsuda, Y. Yaoita, K. Takatsu, and T. Honjo. 1986. Nature 324:70) that amino acids 1-20 serve as the signal sequence for the BCGF-II gene. The ability of BCGF-II to stimulate the proliferation of the B cell lymphoma BCL1 was used to assess the potency of the lymphokine. BCGF-II at 13.5 pM induced 50% of the maximal proliferative response in the BCL1 cells; concentrations as low as 2 pM were still effective in stimulating the growth of the cells. Assuming that the amount of BCGF-II necessary to mount a 50% response in the BCL1 assay is defined as one unit of activity, then the purified BCGF-II has a specific activity of 16.5 U/ng of protein.