The purpose of this Funding Opportunity Announcement (FOA) is to support research that addresses knowledge gaps in the mechanisms of Fc-dependent, antibody-mediated killing of infected or aberrant cells, or antibody-mediated therapeutic ablation of cells implicated in immune pathologies, including autoimmune and allergic diseases. 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 disease). Studies supported under this program will be focused on either or both of two killing mechanisms: antibody dependent cellular cytotoxicity (ADCC) and antibody-dependent cell-mediated phagocytosis (ADCP). There is growing recognition of ADCC and ADCP in humoral control of infection, a research area within the mission of NIAID. Progress in this area will enable more efficient design and optimization of ablative antibody therapeutics and may also inform the design of vaccines that elicit ADCC or ADCP-competent antibody responses.
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 receptor (FcR)-bearing 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 the 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 toin 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 expand our mechanistic understanding of two pathways of Fc-dependent, antibody-mediated killing: ADCC and ADCP. These are highly complex processes that are understudied and for which preliminary data may be severely limited.
This FOA was developed to support high priority research for mechanistic understanding of ADCC and ADCP, translation of mechanistic observations made using in vitro systems for evaluation of in vivo efficacy, and to address complications associated with interpretation of in vivo results. 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, bothin vitro and in vivo . Consensus recommendations for addressing research gaps were incorporated into the list of high priority research areas below.
This initiative will support research that increases our fundamental understanding of ADCC and ADCP. Examples of relevant model systems for functional, mechanistic evaluation of ADCC- and/or ADCP-mediated killing include: cytotoxic killing of infected human cells ( in vitro), in vivo infection models (animal models only), and ex vivo studies using human tissues; the use of model antigens expressed on the target cell surface (which may include tumor antigens); and cytotoxic killing of cells implicated in human immune-mediated disease, (e.g., studies using experimental or licensed human monoclonal antibodies for ablation of cell types associated with autoimmune disease or allergy.)
Under this FOA, high priority research areas include, but are not limited to:
- Hypothesis-driven, mechanistic studies that increase our understanding of the molecular mechanisms of cytotoxic killing by ADCC and/or ADCP. Studies must include evaluation of human monoclonal antibodies. While animal models may be used for in vivo validation, applications should include justification for the proposed animal models, with discussion of their translational relevance to our understanding of ADCC and/or ADCP in humans.
- Descriptive studies to evaluate the contributions of the availability, anatomical distribution and phenotypic characteristics of appropriate effector cell types in human tissues toin vivo killing mechanisms and overall efficacy of therapeutic antibodies. It is expected that knowledge gained through these studies will improve our ability to predict Fc-dependent, cytotoxic functions of antibodies, and will inform design, development and optimization of ablative monoclonal antibody therapeutics for treatment of infectious diseases, autoimmune disease, allergy, and cancer. Results may also inform the design of therapeutic vaccines that preferentially elicit antibodies with Fc-mediated killing functions.
Research topics that fulfill program objectives include, but are not limited to:
- Availability, frequencies, and phenotypes of physiologically relevant human effector cell types at tissue sites, coupled with evaluation of relevant killing mechanisms at sites chosen.
- FcR expression patterns on individual human effector cell types, including:
- Variations in FcR expression patterns among cells of a particular effector cell type, as a function of maturation stage, activation status, and anatomical environment.
- Variations in post-translational modification of FcRs, both within categories of effector cells or among different effector cell types.
- Target antigens and how the nature of epitopes bound by human antibodies affect cytotoxic killing.
- Valency or density of human antibodies bound to epitopes on the target cell.
- Signaling or other biochemical pathways involved in ADCC or ADCP killing.
- Optimal epitope characteristics, which may include: physical distance between the targeted antibody epitope and the target cell membrane; epitope orientation; epitope accessibility, etc.
- Conformational requirements/changes associated with binding of human antibodies to target cells, as required for efficient mediation of ADCC and/or ADCP cytotoxicity.
- Antibody paratope (or (Fab’)2, or idiotype)-associated factors: Antibodies with closely related variable regions may mediate widely variable efficiencies of ADCC or ADCP. Killing efficiencies do not necessarily correlate with affinities of antibody for target antigens, even when specific for the same epitope and bearing identically Fc domains engineered for optimized ADCC or ADCP function.
- Studies to perform 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.
Applications including the following types of studies will be considered non-responsive and will not be reviewed:
- Clinical trials (the NIH definition of clinical trials is available at http://grants.nih.gov/grants/policy/hs/glossary.htm).
- Studies on non-human monoclonal antibodies
- Studies involving antibodies that recognize AIDS, HIV, or SIV epitopes, as studies on killing of HIV-infected cells by HIV-specific antibodies are funded through other solicited research programs.
- Studies exclusively examining antibodies to tumor-associated antigens, unless studies also include other model antigen systems and/or are designed such that results will be more broadly applicable to understanding of ADCC or ADCP-mediated killing in infectious or autoimmune diseases.
- Studies for which the primary objective is the design or development of therapeutic monoclonal antibodies
- Studies solely focused on evaluation of antibody isotype
- 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.
Steering Committee : A Steering Committee (SC) will be formed with the PDs/PIs and NIAID Program Officer to coordinate and facilitate research activities for the overall program; facilitate compliance with the data- and other resource-sharing policies; and promote optimal research flexibility, synergy, and efficiency . Annual Program Progress meetings will be held to discuss the progress of individual research programs. PD(s)/PI(s) are expected to participate in Program Progress meetings by presenting the aims, status and highlights of their project, attend annual face-to-face SC meetings to be held immediately following adjournment of Program Progress meetings, and participate in SC-related activities and teleconference meetings. NIH staff may appoint other subject matter experts as non-voting members of the Steering Committee to provide additional expertise and perspective.
Deadline: January 2, 2019 (letters of intent); February 1, 2019 (full proposals)
Filed Under: Funding Opportunities