Gerald P Morris

University of California, San Diego, San Diego, California, United States

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Publications (27)103.25 Total impact

  • Amritha Balakrishnan · Gerald P. Morris
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    ABSTRACT: Purpose of review: T cells can mediate allograft rejection and graft-versus-host disease (GVHD), but are necessary for tolerance and protective immunity. Identifying T-cell populations differentially responsible for these effects has been a goal in transplant research. This review describes investigation of a small subset of T cells naturally predisposed toward alloreactivity, cells expressing two T-cell receptors (TCRs). Recent findings: Rare peripheral T cells express two αβTCRs. Their impact on T-cell development and function has been uncertain. Recent work demonstrates an important role for these cells in mouse models and human hematopoietic stem cell transplant patients with acute GVHD. Dual receptor T cells are preferentially activated and expanded in vitro and in vivo by allogeneic stimulation. Genetic elimination of dual TCR expression results in loss of approximately half of the alloreactive repertoire and impedes the earliest steps of GVHD. Summary: Identification of dual TCR T cells as predisposed to alloreactivity provides an opportunity to examine responses limiting transplantation. Continued investigation will reveal significant fundamental features of T-cell alloreactivity and important information about the earliest events determining allograft rejection and self-tolerance.
    No preview · Article · Nov 2015 · Current Opinion in Organ Transplantation

  • No preview · Article · Oct 2015 · Human Immunology
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    Burhan P Jama · Gerald P Morris
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    ABSTRACT: The study of human T lymphocyte biology often involves examination of responses to activating ligands. T cells recognize and respond to processed peptide antigens presented by MHC (human ortholog HLA) molecules through the T cell receptor (TCR) in a highly sensitive and specific manner. While the primary function of T cells is to mediate protective immune responses to foreign antigens presented by self-MHC, T cells respond robustly to antigenic differences in allogeneic tissues. T cell responses to alloantigens can be described as either direct or indirect alloreactivity. In alloreactivity, the T cell responds through highly specific recognition of both the presented peptide and the MHC molecule. The robust oligoclonal response of T cells to allogeneic stimulation reflects the large number of potentially stimulatory alloantigens present in allogeneic tissues. While the breadth of alloreactive T cell responses is an important factor in initiating and mediating the pathology associated with biologically-relevant alloreactive responses such as graft versus host disease and allograft rejection, it can preclude analysis of T cell responses to allogeneic ligands. To this end, this protocol describes a method for generating alloreactive T cells from naive human peripheral blood leukocytes (PBL) that respond to known peptide-MHC (pMHC) alloantigens. The protocol applies pMHC multimer labeling, magnetic bead enrichment and flow cytometry to single cell in vitro culture methods for the generation of alloantigen-specific T cell clones. This enables studies of the biochemistry and function of T cells responding to allogeneic stimulation.
    Preview · Article · Nov 2014 · Journal of Visualized Experiments
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    ABSTRACT: Thymic selection is designed to ensure TCR reactivity to foreign Ags presented by self-MHC while minimizing reactivity to self-Ags. We hypothesized that the repertoire of T cells with unwanted specificities such as alloreactivity or autoreactivity are a consequence of simultaneous rearrangement of both TCRα loci. We hypothesized that this process helps maximize production of thymocytes capable of successfully completing thymic selection, but results in secondary TCRs that escape stringent selection. In T cells expressing two TCRs, one TCR can mediate positive selection and mask secondary TCR from negative selection. Examination of mice heterozygous for TRAC (TCRα(+/-)), capable of only one functional TCRα rearrangement, demonstrated a defect in generating mature T cells attributable to decreased positive selection. Elimination of secondary TCRs did not broadly alter the peripheral T cell compartment, though deep sequencing of TCRα repertoires of dual TCR T cells and TCRα(+/-) T cells demonstrated unique TCRs in the presence of secondary rearrangements. The functional impact of secondary TCRs on the naive peripheral repertoire was evidenced by reduced frequencies of T cells responding to autoantigen and alloantigen peptide-MHC tetramers in TCRα(+/-) mice. T cell populations with secondary TCRs had significantly increased ability to respond to altered peptide ligands related to their allogeneic ligand as compared with TCRα(+/-) cells, suggesting increased breadth in peptide recognition may be a mechanism for their reactivity. Our results imply that the role of secondary TCRs in forming the T cell repertoire is perhaps more significant than what has been assumed.
    Preview · Article · Jul 2014 · The Journal of Immunology
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    ABSTRACT: Therapeutic plasma exchange (TPE) is an increasingly utilized immunosuppressive adjunct for treatment of antibody-mediated rejection (AMR) following organ transplantation. TPE works through removal of donor-specific HLA antibodies (DSAs) in the recipient's plasma. However, there is no clear laboratory measure evaluating efficacy of removal of DSAs or predicting clinical outcome. We hypothesized that semi-quantitative DSA measurement by multiplex HLA antibody immunoassay may provide qualitative and quantitative data for DSA clearance and predict treatment efficacy. To evaluate this, we retrospectively investigated DSA concentrations and clinical outcome for 21 pediatric patients who received 31 cycles of TPE peri-operatively as an adjunct treatment for transplantation in the setting of a positive cytotoxic crossmatch (CXM) and in recipients with AMR following heart or lung transplantation. Immunoassay measurement of DSAs during 15/20 cycles correlated significantly with clinical outcome in the AMR treatment group (P = 0.02), demonstrating the utility of DSA measurement in predicting clinical outcome. In contrast, immunoassay correlated with clinical outcome in only 7/11 patients treated peri-operatively with TPE for CXM-positive transplantations (P = 0.58). Changes in mean fluorescence intensity (MFI) for the DSAs correlated better with clinical response than surrogate CXM titers in a subset of patients. We conclude that semi-quantitative measurement of DSAs by immunoassay can predict clinical response to TPE for treatment of AMR is more reliable than surrogate CXM titer, and should be used to guide TPE treatment of AMR. J. Clin. Apheresis, 2013. © 2013 Wiley Periodicals, Inc.
    No preview · Article · Aug 2013 · Journal of Clinical Apheresis
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    ABSTRACT: Acute graft-versus-host disease (aGVHD) results from a robust response of donor T cells transferred during hematopoietic stem cell transplantation (HSCT) to allogeneic peptide-major histocompatibility complex antigens. Previous investigations have not identified T cell subsets that selectively mediate either protective immunity or pathogenic alloreactivity. We demonstrate that the small subset of peripheral T cells that naturally express two T cell receptors (TCRs) on the cell surface contributes disproportionately to aGVHD in patients after allogeneic HSCT. Dual TCR T cells from patients with aGVHD demonstrate an activated phenotype and produce pathogenic cytokines ex vivo. Dual receptor clones from a patient with symptomatic aGVHD responded specifically to mismatched recipient human leukocyte antigens (HLAs), demonstrating pathologic alloreactivity. Human dual TCR T cells are strongly activated and expanded by allogeneic stimulation in vitro, and disproportionately contribute to the repertoire of T cells recognizing both major (HLA) and minor histocompatibility antigens, providing a mechanism for their observed activity in vivo in patients with aGVHD. These results identify dual TCR T cells as a target for focused analysis of a T cell subset mediating GVHD and as a potential prognostic indicator.
    No preview · Article · Jun 2013 · Science translational medicine
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    ABSTRACT: Aim Identification of DSA can be problematic due to antigen saturation in some patients. It is important to identify supplemental methods in order to accurately assess immunologic compatibility. This case demonstrates the utility of sample dilution and the C1qScreen assay (C1q) in providing additional information to accurately assess anti-HLA antibodies (Ab) in a highly-sensitized patient. Methods Patient serum was tested for anti-HLA Ab by Luminex Single Antigen (LSA) and C1q. Serum was tested neat and diluted 1:25. Crossmatch was performed by antihuman globulin-augmented complement-dependent cytotoxicity (AHG). Results Pre-transplant (Tx) LSA identified numerous Class I and II Ab (cPRA = 100). The patient received a lung Tx across known DSA with a strongly positive AHG, T-cell and B-cell positive to 1:512. The patient underwent aggressive immunosuppression and plasma exchange, resulting in stable graft function. Retrospective testing of pre-Tx serum by LSA at 1:25 dilution, and C1q, demonstrated strong DSA. Evaluation on post-op day 52 demonstrated reduced overall anti-HLA Ab with persistent Class II DSA (cPRA = 95) by LSA, not seen on C1q testing. Post-op day 261 showed the first evidence of no DSA by LSA, with continued graft function. Conclusions Prognostic identification of clinically-relevant Ab may require multiple test methods. Ab identified by C1q may more accurately reflect post-Tx compatibility [Table 1 and Table 2].
    No preview · Article · Oct 2012 · Human Immunology
  • Article: 177-P

    No preview · Article · Oct 2012
  • Article: 178-P

    No preview · Article · Oct 2012
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    ABSTRACT: Application of single-antigen solid-phase immunoassay (SPI) in virtual crossmatch-based organ allocation has been hindered by continued debate over the biologic relevance of detected antibodies and the relationship between cutoff mean fluorescence intensity (MFI) values with crossmatch testing results. To define SPI parameters accurately predicting crossmatch testing, we analyzed a series of anti-HLA antibodies from highly-sensitized patients awaiting lung or heart transplantation. Serial dilution of serum for SPI and cytotoxic crossmatch (CXM) enabled comparison over a wide spectrum of antibody "strengths". Receiver operating characteristic (ROC) analysis identified predictive cutoff values for HLA Class I and DR-specific antibodies. However, antibodies to HLA-DQ antigens demonstrated a significantly different characteristic, highlighting difficulties in interpretation of clinical significance. We also quantitatively characterized two data handling methods, MFI ratio (MR) and relative ratio (RR), to examine their potential impact on identifying unacceptable antigens. In combination with user defined cutoff values, MFI, MR and RR lead to discordant identification of antibodies. Establishment of cutoff values for MR and RR that are comparable to MFI demonstrated increased consistency in antibody identification. This single laboratory experience is an example of establishing statistically robust cutoff values and validation across different data handling methods for use of SPI in virtual crossmatch.
    Full-text · Article · Apr 2012 · Human immunology
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    Gerald P Morris · Paul M Allen
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    ABSTRACT: The T cell repertoire is generated during thymic development in preparation for the response to antigens from pathogens. The T cell repertoire is shaped by positive selection, which requires recognition by the T cell antigen receptor (TCR) of complexes of self peptide and major histocompatibility complex proteins (self-pMHC) with low affinity, and negative selection, which eliminates T cells with TCRs that recognize self-pMHC with high affinity. This generates a repertoire with low affinity for self-pMHC but high affinity for foreign antigens. The TCR must successfully engage both of these ligands for development, homeostasis and immune responses. This review discusses mechanisms underlying the interaction of the TCR with peptide-major histocompatibility complex ligands of varying affinity and highlights signaling mechanisms that enable the TCR to generate different responses to very distinct ligands.
    Preview · Article · Feb 2012 · Nature Immunology
  • Ronald Jackups Jr · Gerald Morris

    No preview · Article · Oct 2011 · Human Immunology

  • No preview · Article · Oct 2011 · Human Immunology

  • No preview · Article · Oct 2011 · Human Immunology
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    Gerald P Morris · Peggy P Ni · Paul M Allen
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    ABSTRACT: A significant portion of the naive T-cell repertoire is capable of responding to allogeneic MHC, violating the paradigm of self-MHC restriction. Recent studies have demonstrated convincing evidence for germ-line affinity of T-cell receptors (TCR) for MHC, providing explanation for recognition of MHC not encountered during thymic development. However, although germ-line affinity proposes all TCR have inherent affinity for MHC, most T cells are not alloreactive to a given MHC. We propose that specific recognition of endogenous presented peptides, rather than inability to interact with allogeneic MHC molecules, is the primary determinant of alloreactivity. Here, we demonstrate that alloreactive and nonalloreactive TCR differ specifically in the CDR3 sequences responsible primarily for the peptide specificity of T-cell recognition. Limitations on alloreactivity imposed by a requirement for recognition of presented peptides are directly demonstrated by expansion of the alloreactive T-cell repertoire through the addition of peptide mimotopes enabling response to two distinct allogeneic MHC by otherwise nonalloreactive T cells. Responses to peptide mimotopes were specific and depended on TCR interaction with MHC. These results demonstrate that recognition of presented endogenous peptides, and not the inability to interact with allogeneic MHC, is the primary limiter on alloreactivity. This observation reconciles the concept of an inherently MHC-reactive TCR repertoire with observed frequencies of T cells responding to allogeneic stimulation and underscores the fundamental nature of TCR recognition of ligands, where both MHC and presented peptides contribute critically to T-cell recognition.
    Preview · Article · Feb 2011 · Proceedings of the National Academy of Sciences
  • Gerald P. Morris · T. Mohanakumar
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    ABSTRACT: The presence of preformed antibodies against alloantigens has been clearly demonstrated to be the primary barrier to successful allogeneic solid organ transplantation. While antibodies to Human Leukocyte Antigens are the antibodies most closely associated with both hyperacute, acute, and chronic antibody mediated rejection, antibodies to numerous other alloantigens have been described. Antibodies against the ABO system antigens, MICA, and endothelial cell antigens have all been described as mediators of humoral rejection of solid organ grafts. The important role of alloantibody in mediating immunologic rejection has led to the development of highly sensitive and robust methods for detection and definition of alloantibody in both pre and posttransplant patients. Sensitive and accurate detection of alloantibody, as well as accurate interpretation of the results, is critical to maximize the success of allogeneic solid organ transplantation.
    No preview · Article · Jan 2011

  • No preview · Article · Sep 2010 · Human Immunology
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    ABSTRACT: Patients suffering from sepsis are currently classified on a clinical basis (i.e., sepsis, severe sepsis, septic shock); however, this clinical classification may not accurately reflect the overall immune status of an individual patient. Our objective was to describe a cohort of patients with sepsis in terms of their measured immune status. Fifty-two patients with sepsis (n = 13), severe sepsis (n = 21), or septic shock (n = 18) were studied. The immune status was determined by measuring the CD4+ lymphocyte adenosine triphosphate (ATP) content after mitogen stimulation in whole blood. The measured CD4+ lymphocyte ATP content at the time of ICU admission did not differ among the various groups defined by the sepsis classification system (sepsis = 454 +/- 79 ng/ml; severe sepsis = 359 +/- 54 ng/ml; septic shock = 371 +/- 53 ng/ml; P = 0.44). Furthermore, survivors of sepsis had a significantly higher CD4+ lymphocyte ATP content at the time of ICU admission than did nonsurvivors of sepsis (431 +/- 41 ng/mL vs. 266 +/- 53 ng/mL, respectively; P = 0.04). The sepsis classification system that is currently used is not representative of the individual immune status as determined by measuring the CD4+ lymphocyte ATP content. Moreover, a lower CD4+ ATP content at the time of ICU admission is associated with a worse clinical outcome in those suffering from sepsis.
    Preview · Article · Jun 2010 · Critical care (London, England)
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    ABSTRACT: Selection of donors for kidney transplantation depends on accurate prediction of risk factors for immunologic rejection. Historically, cytotoxicity crossmatch (CXM) examining lysis of donor cells by preformed anti-human leukocyte antigen (HLA) antibodies (Abs) has been considered the best predictor of immunologic rejection. However, there is much interest in defining anti-HLA Ab specificity in recipient sera by immunoassay to predict crossmatch results and aid in donor selection. Current immunoassays for anti-HLA Abs are highly sensitive, though correlation between Abs detected by immunoassay and their functional relevance in CXM and subsequent transplantation is not well defined. In this study, we retrospectively examined the predictive value of detection of donor-specific anti-HLA Abs (DSA) by Luminex Single Antigen assay from 149 consecutive living donor kidney transplant recipients. We demonstrate that detection of DSA by immunoassay accurately predicted negative crossmatch and graft survival. However, this approach had limited sensitivity for predicting positive crossmatch, attributable to either limited typing of donor HLA-DQ and -DP alleles or due to non-HLA Abs. False-positive prediction of CXM correlated with detection of "weak" Abs with low mean fluorescence intensity (MFI < 2000). Furthermore, we found that a ratio of the MFI of the DSA bead to the MFI of the positive control bead was a better method for identifying weak DSA that did not result in CXM-positive reactions. Interestingly, patients with weak DSA and negative CXM had equivalent graft survival over an 18 month follow-up period, suggesting that weak DSA may not preclude transplantation.
    No preview · Article · Mar 2010 · Human immunology
  • J. Jennemann · D. Phelan · R. Hill · P. Willey · G. Morris

    No preview · Article · Nov 2009 · Human Immunology

Publication Stats

215 Citations
103.25 Total Impact Points


  • 2014-2015
    • University of California, San Diego
      San Diego, California, United States
  • 2008-2013
    • Washington University in St. Louis
      • Department of Pathology and Immunology
      San Luis, Missouri, United States