NIH – Fc-Dependent Mechanisms of Antibody-Mediated Killing (R21 Clinical Trial Not Allowed)

Note:  a U01 version of a very similar also was announced by NIH this month.

The purpose of this Funding Opportunity Announcement (FOA) is to advance research that improves our understanding of Fc-dependent, antibody-mediated killing of pathogen-infected or otherwise dysregulated host cells. More specifically, this FOA promotes innovative and/or exploratory studies to elucidate basic mechanisms of antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cell-mediated phagocytosis (ADCP), and development of tools, technologies, and animal models to facilitate identification and evaluation of cytotoxic killing mechanisms mediated by human antibodies in vivo. Targets of therapeutic, Fc-dependent, antibody-mediated killing include: pathogen-infected cells, malignant cells, and host cells implicated in immune pathologies (e.g., autoimmune and allergic diseases). Increased understanding of ADCC and ADCP will inform the design of vaccines that elicit ADCC- or ADCP-competent antibody responses and will enable more efficient optimization of ablative antibody therapeutics.

Background

Therapeutic monoclonal antibodies have shown much promise for the treatment of infectious and immune-mediated diseases and cancer. Antibodies contain two general types of domains; a bivalent F(ab’)2 domain that is highly variable and responsible for the ability of antibodies to recognize an extraordinarily large universe of antigens, and a constant (Fc) region associated with functional activities. The subclass or isotype of the Fc region influences functional capabilities of the antibody. Among these functions are killing of pathogens or infected host cells through complement-mediated killing or killing of cells through binding of Fc domains to Fc receptors (FcR) on effector cells.

There is growing recognition of the importance of two Fc/FcR-dependent mechanisms of antibody-mediated protection in the destruction of infected host cells. These mechanisms are dependent upon recruitment of effector cells bearing FcRs that, upon interaction with the Fc domains of antibodies bound to infected cells, are activated to deploy cytotoxic programs to destroy their targets.

The first mechanism is antibody-dependent cellular cytotoxicity (ADCC). Multiple effector cell types are competent to kill target cells via ADCC, at least under in vitro assay conditions. These cell types include: NK cells, neutrophils, macrophages, monocytes and eosinophils. These FcR-bearing effectors kill their targets through release of cytotoxic molecules following engagement of their FcRs by antibodies bound to the target cell surface.

The second mechanism is antibody-dependent cell-mediated phagocytosis (ADCP). Multiple FcR-bearing effector cell types have demonstrated proficiency in ADCP, including neutrophils, macrophages, monocytes, and dendritic cells. In these cases, Fc/FcR interactions between target bound antibodies and FcR-bearing effector cells promote engulfment and destruction of target cells by effector cells.

For therapeutic applications, monoclonal antibody development is commonly focused on cytotoxic destruction of infected, malignant, or pathogenic host cells. On infected cells, the target antigen may be a pathogen-derived epitope displayed on the cell surface. For malignant cells, it may be a tumor-associated antigen. In the case of autoimmune or allergic disease, the antibody therapeutic may be used for selective ablation of cell types responsible for immune pathology.

The importance of antibody isotype and glycosylation status on ADCC and ADCP efficiencies is widely recognized, and these two parameters are active areas of research. However, it is still difficult to predict ADCC or ADCP killing efficiencies based on antibody isotype and Fc glycosylation patterns alone, making it challenging to reliably design antibodies that mediate Fc-dependent killing in vivo . For example, antibodies that recognize identical or overlapping epitopes on a target cell antigen may have dramatically different abilities to mediate ADCC or ADCP, even when they are engineered to have identical Fc regions and glycosylation patterns. In addition, the relative contribution of each killing mechanism to in vivo efficacy is difficult to evaluate and may vary even within an individual, depending on anatomical location and microenvironment of target cells. A key microenvironmental variable is the availability and type of effector cells required for Fc/FcR-mediated killing. Preliminary evaluation of antibody therapeutics continues to rely on empirical testing of each antibody for cytotoxic activities under in vitro assay conditions. Even when ADCC-competent antibodies are identified and optimized for highly efficient in vitro killing, the results often fail to translate to in vivo efficacy.

Elevation of NK cell numbers during infection has led to speculation that they may serve as primary effector cells for ADCC. However, NK cells have additional antibody-independent roles in innate control of infection and their increased frequencies may be independent of potential roles as effector cells for ADCC-mediated killing in vivo. Importantly, closer consideration must be given to the role of other cell types present at sites of infection as potential effectors of antibody-mediated killing. For example, alveolar macrophages may play critical roles in the control of respiratory infection through ADCC, ADCP, or both killing mechanisms. In fact, cancer studies suggest that while NK cells are the most commonly used effector cells for in vitro ADCC assays, monocytes and macrophages are often identified to be the main effectors of antibody-mediated killing of cancer cells in vivo.

Research Objectives and Scope

The goal of this initiative is to support exploratory studies to expand our mechanistic understanding of two pathways of Fc-dependent, antibody-mediated killing: ADCC and ADCP; and to support the development of tools and animal models to facilitate the identification of mechanisms of Fc-dependent antibody-mediated killing in vivo. These are highly complex processes that are understudied and for which preliminary data may be severely limited. Because there are still large gaps in our understanding of ADCC and ADCP, both descriptive and hypothesis driven research is acceptable under this FOA and preliminary data are not required.

This FOA conveys NIAID’s interest in research designed to increase our fundamental understanding of ADCC and/or ADCP.  While long-range goals are to understand factors that influence killing efficiencies in vivoin vitro studies designed to evaluate contributions of individual variables to killing functions are also strongly encouraged.

In June 2017, NIAID assembled a group of external scientists representing academic, biotechnology and pharmaceutical sectors to identify research gaps that should be addressed to accelerate our understanding of the mechanisms of ADCC and ADCP, both in vitro and in vivo. Examples of research that address gaps in our understanding of ADCC and ADCP in humans and animal models include, but are not limited to:

  • Studies designed to evaluate in vivo availability, frequencies, and phenotypes of individual effector cell types under normal and/or pathological conditions
  • Evaluation of plasticity in FcR expression and/or glycosylation as functions of effector cell type, effector cell development/differentiation/subset, effector cell activation, and anatomical location
  • Exploratory studies to evaluate variables affecting efficiencies of killing through ADCC and/or ADCP, including:
  1. Examination of killing mechanisms as functions of antigen/epitope characteristics
  2. Characterization of the roles of epitope orientation, distance from the target and/or effector cell membrane, etc. on killing efficiencies
  3. Evaluation of relationships between antigen density on target cell surface and killing efficiencies
  4. Examination of how antibody affinity influences mechanisms of cytotoxic killing and/or killing efficiency
  5. Studies on how conformational changes in antibodies following binding to target cells influences mechanism of killing or killing efficiency
  6. Paratope studies to determine why two (or more) antibodies that bind to identical or overlapping epitopes may have dramatically different abilities to mediate ADCC or ADCP, even when Fc domains are comparable.
  7. Comparative, mechanistic evaluation of ADCC and/or ADCP using existing antibody collections obtained during design or development of therapeutic monoclonal antibodies are acceptable, with strong justification for the value of the antibody collection(s) for proposed hypothesis-driven, mechanistic research.
  • Development of tools, techniques, and animal models to enable identification of antibody-mediated killing mechanism(s) responsible for in vivo killing by human antibodies.

Research areas NOT appropriate for this FOA include:

  • Studies for which the primary objective is the design or development of therapeutic monoclonal antibodies
  • Studies solely focused on evaluation of antibody isotype, without detailed structural mechanistic analyses.
Studies solely focused on antibody glycosylation, as such studies on the roles of glycosylation of cytotoxic killing are already supported through active investigator-initiated grants and other solicited research programs.

Deadlines:  standard dates and standard AIDS dates apply

URL:  https://grants.nih.gov/grants/guide/pa-files/PA-19-020.html