Division of Pulmonary, Allergy
and Critical Care Medicine
Research Laboratories
Raphael A. Clynes, M.D.,
Ph.D.
Assistant
Professor of Medicine, Division of Pulmonary, Allergy and Critical Care
Medicine
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Laboratory Address 630 Phone 212-305-5289 Fax 212-305-1392 |
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The research focus of the laboratory is to define the mechanisms of
antibody-mediated cytotoxicity as applied to both
tumor immunity and immune complex disease. We have shown using genetic
studies in mice that the cellular receptors for IgG
(Fc receptors) modulate the host response triggered
by immune complexes and cellular bound antibody. The human and mouse IgG Fc receptor (FcgammaR) family are highly conserved and all murine FcgammaR family members
have homologous counterparts in the human system. Both systems share both
activating and inhibitory receptors for IgG. The
activating receptors for IgG, FcgammaRI
and FcgammaRIII both require an additional chain,
the gamma subunit, for receptor signaling and assembly. The third receptor
for IgG, FcgammaRII, is
an inhibitory receptor; receptor coligation of FcgammaRII to either activating receptor FcgammaRI or III, results in down-modulation of the
activation signals. The co-expression of both activating and inhibitory Fc receptors on the membrane of hematopoietic
cells suggests that the coordinated regulation of these receptors alters the
threshold of IC-mediated activation thereby setting the state of cellular
IC-responsiveness. Our studies of IgG-triggered effector responses in gene targeted mice have revealed
this balanced regulation of IC-effector responses
by the opposing effects of genetic disruption of the activating and
inhibitory FcgammaR pathways. In models of autoimmunity, mice deficient in the activating Fc receptors are protected from immune complex-triggered
inflammatory responses whereas mice lacking inhibitory Fc
receptors exhibit dramatically enhanced inflammatory responses. Furthermore
the protective anti-tumor responses provided by anti-melanoma, lymphoma and
breast adenocarcinoma monoclonal antibodies require
Fc receptor interactions in vivo whereas the
biological tumorocidal activity of these antibodies
are more than 10-fold enhanced in mice lacking inhibitory Fc
receptors. These studies indicate that the threshold of activation triggered
by IgG immune complexes is determined by the
modulated expression of both activating and inhibitory Fc
receptors on cellular effectors. We are interested in determining the
identity of these Fc receptor-bearing effector cells that are responsible for both IgG mediated anti-tumor effects and autoimmune
inflammation as well as the molecular mediators employed by the effector cell arsenal which lead to target cell-death. Antibody-Mediated
Tumor Immunity Effective immunity against neoplastic
disease requires the specific recognition of tumor antigens coupled with the
activation of the effector cytotoxic
response. The understanding of the common underlying cytotoxic
mechanisms elicited by these approaches would provide the basis for attempts
to improve the efficacy of tumor immunotherapeutics. We are interested in defining the molecular mechanisms of
antibody-mediated cytotoxicity (ADCC) by
identifying the roles of specific inhibitory and activating cellular
receptors for IgG, the effector
cell type responsible for ADCC in vivo and the molecular mechanisms employed
by these effectors to kill tumor target cells. Recently we have demonstrated
that the disruption of the activation FcR pathway
was sufficient to completely abrogate tumor protection afforded by several
monoclonal antibody anti-tumor antibodies including 1) anti-melanoma
monoclonal and polyclonal antibodies in a mouse melanoma pulmonary metastases
model and 2) anti-HER2/neu and anti-CD20 mAbs in xenograft nude mouse models of human breast cancer and
lymphoma. Conversely in mice that lack the inhibitory receptor for IgG the efficacy of antitumor
antibodies is dramatically enhanced. Most effector
cells (including neutrophils and monocytes) express both activating and inhibitory Fc Receptors. Thus the threshold of effector
cell activation by IgG is determined by the
balanced ouput of these two opposing signaling
pathways. These data demonstrate an unexpected and critical role for
activating/inhibitory FcgammaRs in modulating tumor
cytotoxicity in vivo and suggest that enhancement
of FcgammaR-mediated an
body-dependent cellular cytotoxicity by
inflammatory cells is a key step in the development of effective
antibody-mediated immunotherapeutics. Immune
Complex Disease The immune complex triggered inflammatory response is the pathogenic
mechanism of tissue injury in a number of autoimmune diseases including
arthritis, vasculitis and glomerulonephritis
(GN). In particular the deposition of circulating DNA-antiDNA
immune complexes leads to the development of vascular and glomerular
lesions in SLE. The "Lupus-prone" NZB/NZW mouse model shares
several pathogenic and genetic similarities with human S.L.E. including a
female bias, and the appearance of IgG containing
pathogenic anti-DNA autoantibodies which heralds
the onset of severe rapidly progressive GN. The disease process may be
separated into two processes: the afferent limb of autoantibody production
with concomitant generation and tissue deposition of circulating immune
complexes and the subsequent effector limb of the
inflammatory response elicited by ICs. Since immune complex tissue deposits
avidly fix complement, the effector responses may
be triggered by either cellular Fc receptors or by
complement mediated pathways. The importance of the Fc
receptor effector pathway in modulating immune
complex inflammation has been established in mice bearing targeted
disruptions in FcR genes. In these gamma -/- mice
the afferent limb of autoimmunity is intact but the subsequent inflammatory
response is uncoupled. Thus gamma -/- mice are protected from autoimmune
injury in models of autoimmune hemolytic anemia, autoimmune thrombocytopenia,
and from immune complex injury in the lung, kidney and skin. Both NZB/NZW
gamma -/- and +/+ mice develop autoantobodies with glomerular deposition of immune complexes but the
uncoupling of the effector response prevents the
development of fatal nephritis in g -/-. These studies challenge the
prevailing view that complement components are sufficient to initiate
IC-mediated inflammatory responses and argue for the development of FcR targeted therapeutics in the treatment of immune
complex mediated disease. Immune complex injury may result from activation of resident tissue
inflammatory cells and/or the recruitment of circulating monocytes
or neutrophils to sites of deposition. In the
kidney, activation and proliferation of the resident mesangial
cell is a hallmark of immune complex inflammatory disease. Because of this
circularity of the proinflammatory cytokine network
it is unclear which cell(s) are critical to the initiation of the
inflammatory cascade. Since Fc receptors are
expressed on most leukocytes, including monocytes
and neutrophils, and may also be expressed on
resident mesangial cells, a number of potential
initiation pathways are possible. The identification of specific FcR-bearing effector cells
responsible for the initiation of this clinically relevant IC-mediated
disease will have general implications for the understanding of mechanisms
underlying systemic autoimmune disease. |
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