Heterotopic Auxiliary Whole Liver Rat Transplant Model Utilizing a Hepaticoureterostomy for Allograft Rejection Studies.

Small animal transplant models are indispensable for organ tolerance studies investigating feasible therapeutic interventions in preclinical studies. Rat liver transplantation (LTx) protocols typically use an orthotopic model where the recipients' native liver is removed and replaced with a donor liver. This technically demanding surgical procedure requires advanced micro-surgical skills and is further complicated by lengthy anhepatic and lower body ischemia times. This prompted the development of a less complicated heterotopic method that can be performed faster with no anhepatic or lower body ischemia time, reducing post-surgery stress for the recipient animal. This heterotopic LTx protocol includes two main steps: excising the liver from the donor rat and transplanting the whole liver into the recipient rat. During the excision of the donor liver, the surgeon ligates the supra-hepatic vena cava (SHVC) and hepatic artery (HA). On the recipient side, the surgeon removes the left kidney and positions the donor liver with the portal vein (PV), infra-hepatic vena cava (IHVC), and bile duct facing the renal vessels. Further, the surgeon anastomoses the recipient's renal vein end to end with the IHVC of the liver and arterializes the PV with the renal artery using a stent. A hepaticoureterostomy is utilized for biliary drainage by anastomosing the bile duct to the recipient's ureter, permitting the discharge of bile via the bladder. The average duration of the transplantation was 130 min, cold ischemia duration was around 35 min, and warm ischemia duration was less than 25 min. Hematoxylin and eosin histology of the auxiliary liver from syngeneic transplants showed normal hepatocyte structure with no significant parenchymal alterations 30 days post-transplant. In contrast, 8-day post-transplant allogeneic graft specimens demonstrated extensive lymphocytic infiltration with a Banff Schema rejection activity index score of 9. Therefore, this LTx method facilitates a low morbidity rejection model alternative to orthotopic LTx.

APRIL/BLyS deficient rats prevent donor specific antibody (DSA) production and cell proliferation in rodent kidney transplant model.

APRIL (A proliferation inducing ligand) and BLyS (B Lymphocyte Stimulator) are two critical survival factors for B lymphocytes and plasma cells, the main source of alloantibody. We sought to characterize the specific effects of these cytokines in a kidney transplant model of antibody mediated rejection (AMR). We engineered APRIL-/- and BLyS-/- Lewis rats using CRISPR/Cas9. APRIL-/- and BLyS-/- rats were sensitized with Brown Norway (BN) blood (complete MHC mismatch). Twenty-one days following sensitization, animals were harvested and collected tissues were analyzed using flow cytometry, ELISPOT, and immunohistochemistry. Flow cross match and a 3 day mixed lymphocyte reaction (MLR) was performed to assess donor specific antibody (DSA) production and T-cell proliferation, respectively. Sensitized dual knock out Lewis rats (APRIL-/-/BLyS-/-) underwent kidney transplantation and were sacrificed on day 7 post-transplant. Sensitized BLyS-/- had significant decreases in DSA and cell proliferation compared to WT and APRIL-/- (p<0.02). Additionally, BLyS-/- rats had a significant reduction in IgG secreting cells in splenic marginal zone B lymphocytes, and in cell proliferation when challenged with alloantigen compared to WT and APRIL-/-. Transplanted APRIL-/-/BLyS-/- rodents had significantly less DSA and antibody secreting cells compared to WT (p<0.05); however, this did not translate into a significant difference in AMR seen between groups. In summary, our studies suggest that APRIL and BLyS play a greater role in DSA generation rather than AMR, highlighting the role of cellular pathways that regulate AMR.

The Immunological Effect of Oxygen Carriers on Normothermic Ex Vivo Liver Perfusion.

Introduction: Normothermic ex vivo liver perfusion (NEVLP) is an organ preservation method that allows liver graft functional assessment prior to transplantation. One key component of normothermic perfusion solution is an oxygen carrier to provide oxygen to the liver to sustain metabolic activities. Oxygen carriers such as red blood cells (RBCs) or hemoglobin-based oxygen carriers have an unknown effect on the liver-resident immune cells during NEVLP. In this study, we assessed the effects of different oxygen carriers on the phenotype and function of liver-resident immune cells. Methods: Adult Lewis rat livers underwent NEVLP using three different oxygen carriers: human packed RBCs (pRBCs), rat pRBCs, or Oxyglobin (a synthetic hemoglobin-based oxygen carrier). Hourly perfusate samples were collected for downstream analysis, and livers were digested to isolate immune cells. The concentration of common cytokines was measured in the perfusate, and the immune cells underwent phenotypic characterization with flow cytometry and quantitative reverse transcription polymerase chain reaction (qRT-PCR). The stimulatory function of the liver-resident immune cells was assessed using mixed lymphocyte reactions. Results: There were no differences in liver function, liver damage, or histology between the three oxygen carriers. qRT-PCR revealed that the gene expression of nuclear factor κ light chain enhancer of activated B cells (NF-kB), Interleukin (IL-1ß), C-C motif chemokine ligand 2 (CCL2), C-C motif chemokine ligand 7 (CCL7), and CD14 was significantly upregulated in the human pRBC group compared with that in the naive, whereas the rat pRBC and Oxyglobin groups were not different from that of naive. Flow cytometry demonstrated that the cell surface expression of the immune co-stimulatory protein, CD86, was significantly higher on liver-resident macrophages and plasmacytoid dendritic cells perfused with human pRBC compared to Oxyglobin. Mixed lymphocyte reactions revealed increased allogeneic T-cell proliferation in the human and rat pRBC groups compared to that in the Oxyglobin group. Conclusions: Liver-resident immune cells are important mediators of rejection after transplantation. In this study, we show that the oxygen carrier used in NEVLP solutions can affect the phenotype of these liver-resident immune cells. The synthetic hemoglobin-based oxygen carrier, Oxyglobin, showed the least amount of liver-resident immune cell activation and the least amount of allogeneic proliferation when compared to human or rat pRBCs. To mitigate liver-resident immune cell activation during NEVLP (and subsequent transplantation), Oxyglobin may be an optimal oxygen carrier.

Single-cell RNA sequencing distinguishes dendritic cell subsets in the rat, allowing advanced characterization of the effects of FMS-like tyrosine kinase 3 ligand.

Tissue-resident dendritic cells (DCs) are essential for immunological homeostasis and hold promise for a variety of therapeutic interventions. The rare nature of tissue-resident DCs and their suboptimal description in the lab rat model has limited their characterization. To address this limitation, FMS-like tyrosine kinase 3 ligand (FLT3L) has been utilized to expand these population in vitro and in vivo for investigative or therapeutic purposes. However, conflicting reports have suggested that FLT3L can either promote immune tolerance or enhance immunogenicity, necessitating clarification of the effects of FLT3L on DC phenotype and functionality. We first paired single-cell RNA sequencing with multicolour spectral flow cytometry to provide an updated strategy for the identification of tissue-resident classical and plasmacytoid DCs in the rat model. We then administered FLT3L to Lewis rats in vivo to investigate its effect on tissue-resident DC enumeration and phenotype in the liver, spleen, and mesenteric lymph nodes. We found that FLT3L expands classical DCs (cDCs) 1 and 2 in a dose-dependent manner and that cDC1 and cDC2 in secondary lymphoid organs had altered MHC I, MHC II, CD40, CD80, CD86, and PD-L1 cell-surface expression levels following FLT3L administration. These changes were accompanied by an increase in gene expression levels of toll-like receptors 2, 4, 7, and 9 as well as inflammatory cytokines IL-6 and TNF-α. In conclusion, FLT3L administration in vivo increases cDC enumeration in the liver, spleen, and mesenteric lymph nodes accompanied by a tissue-restricted alteration in expression of antigen presentation machinery and inflammatory mediators.

Suppression of Inflammation-Associated Kidney Damage Post-Transplant Using the New PrC-210 Free Radical Scavenger in Rats.

Allograft kidney transplantation, which triggers host cellular- and antibody-mediated rejection of the kidney, is a major contributor to kidney damage during transplant. Here, we asked whether PrC-210 would suppress damage seen in allograft kidney transplant. Brown Norway (BN) rat kidneys were perfused in situ (UW Solution) with or without added 30 mM PrC-210, and then immediately transplanted into Lewis (LEW) rats. 20 h later, the transplanted BN kidneys and LEW rat plasma were analyzed. Kidney histology, and kidney/serum levels of several inflammation-associated cytokines, were measured to assess mismatch-related kidney pathology, and PrC-210 protective efficacy. Twenty hours after the allograft transplants: (i) significant histologic kidney tubule damage and mononuclear inflammatory cell infiltration were seen in allograft kidneys; (ii) kidney function metrics (creatinine and BUN) were significantly elevated; (iii) significant changes in key cytokines, i.e., TIMP-1, TNF-alpha and MIP-3A/CCL20, and kidney activated caspase levels were seen. In PrC-210-treated kidneys and recipient rats, (i) kidney histologic damage (Banff Scores) and mononuclear infiltration were reduced to untreated background levels; (ii) creatinine and BUN were significantly reduced; and (iii) activated caspase and cytokine changes were significantly reduced, some to background. In conclusion, the results suggest that PrC-210 could provide broadly applicable organ protection for many allograft transplantation conditions; it could protect transplanted kidneys during and after all stages of the transplantation process-from organ donation, through transportation, re-implantation and the post-operative inflammation-to minimize acute and chronic rejection.

Interleukin-10 and Transforming Growth Factor-ß Cytokines Decrease Immune Activation During Normothermic Ex Vivo Machine Perfusion of the Rat Liver.

Normothermic ex vivo liver perfusion (NEVLP) is a novel system for organ preservation that may improve over static cold storage clinically and offers the chance for graft modification prior to transplantation. Although recent studies have shown the presence of inflammatory molecules during perfusion, none have yet shown the effects of NEVLP on liver-resident immune cell activation. We investigated the effects of NEVLP on liver-resident immune cell activation and assessed the ability of anti-inflammatory cytokines interleukin 10 (IL10) and transforming growth factor ß (TGF-ß) to improve organ function and reduce immune activation during perfusion. Rat livers were perfused for 4 hours at 37°C with or without the addition of 20 ng/mL of each IL10 and TGF-ß (n = 7). Naïve and cold storage (4 hours at 4°C) livers served as controls (n = 4). Following preservation, gene expression profiles were assessed through single-cell RNA sequencing; dendritic cell and macrophage activation was measured by flow cytometry; and cytokine production was assessed by enzyme-linked immunosorbent assay. NEVLP induced a global inflammatory gene expression signature, most notably in liver-resident macrophages and dendritic cells, which was accompanied by an increase in cell-surface levels of major histocompatibility complex (MHC) II, CD40, and CD86. Immune activation was partially ameliorated by IL10 and TGF-ß treatment, but no changes were observed in inflammatory cytokine production. Overall levels of liver damage and cellular apoptosis from perfusion were low, and liver function was improved with IL10 and TGF-ß treatment. This is the first study to demonstrate that liver-resident immune cells gain an activated phenotype during NEVLP on both the gene and protein level and that this activation can be reduced through therapeutic intervention with IL10 and TGF-ß.

Significant Improvement in Rat Kidney Cold Storage Using UW Organ Preservation Solution Supplemented With the Immediate-Acting PrC-210 Free Radical Scavenger.

Ischemia-reperfusion injury, including injury from warm- and cold-ischemia (CI) organ storage, remains a significant problem for all solid organ transplants. Suppressing CI damage would reduce delayed graft function and increase the donor organ pool size. PrC-210 has demonstrated superior prevention of damage in several preclinical studies as an immediate-acting free-radical scavenger. Here, we describe its profound efficacy in suppressing CI injury in a rat kidney model. METHODS: Kidneys in 300 gm Sprague-Dawley rats were perfused in situ with UW solution with or without added PrC-210 and then stored at 4°C in the same solution for 0 to 48 hours. When procured, kidney-activated caspase-3 level (a marker of cell death) was measured, and direct histological analysis of kidneys was performed to assess PrC-210 protective efficacy. In vitro analyses of PrC-210-conferred protection to isolated rat kidneys or naked DNA were also performed. RESULTS: A single 15 seconds in situ perfusion of kidneys with 20 mmol/L PrC-210 in UW solution resulted in significant reductions in (1) 30-hour CI-induced kidney-activated caspase level (P < 0.0001); activated caspase was reduced to levels not significantly different than control activated caspase levels seen in unperturbed kidneys, (2) 30-hour CI-induced renal Tubular Injury Scores (P = 0.0004) where brush border and tubular necrosis were markedly reduced, (3) PrC-210 conferred 100% protection against ·OH damage to naked DNA and isolated kidney mitochondria while current UW solution antioxidants were without protective effect. CONCLUSIONS: A single PrC-210-UW solution perfusion of rat kidneys upon removal from the rat profoundly reduced caspase and renal tubular injury in kidneys exposed to 30 hours of CI organ storage. These findings support further development of the PrC-210 molecule to suppress or to prevent ischemia-reperfusion injury in organ transplant and other ischemia-reperfusion injury settings.

Oxidized-ATP Attenuates Kidney Allograft Rejection By Inhibiting T-Cell, B-Cell, and Macrophage Activity.

Background: Extracellular ATP binds to purinergic receptors and promotes inflammatory responses. We tested whether oxidized ATP (oATP), P2X7 receptor antagonist can attenuate acute kidney allograft rejection. Methods: Brown Norway kidney allografts were transplanted into Lewis recipients. Three groups were defined: oATP (n=8), cyclosporine A (n=6), and no treatment (n=8). On day 7, we assessed kidney allograft survival, function, and rejection characteristics. We further determined T-cell, B-cell, and macrophage response to oATP in vivo and in vitro and examined intragraft inflammatory gene transcripts. Results: Kaplan-Meier survival analyses demonstrated significantly better graft survival rates in oATP and CsA groups compared with no treatment (P<0.05). Similarly, serum creatinine (Scr) and BUN levels were significantly lower in oATP and CsA groups (P<0.05). oATP reduced both T cell-mediated rejection and antibody-mediated rejection, inhibited B-cell and T-cell activation, and downregulated intragraft IL-6 mRNA levels (P<0.0001). In vitro, oATP prevented proliferation in mixed lymphocyte reaction assays, and inhibited macrophage P2X7R activity in a dose-dependent manner. Conclusions: Our findings suggest that oATP mitigates kidney allograft rejection by inhibiting T-cell, B-cell, and macrophage activity and indicate a potential role for the purinergic system and oATP in solid organ transplantation.

Autoantibody production significantly decreased with APRIL/BLyS blockade in murine chronic rejection kidney transplant model.

Chronic antibody mediated rejection (cAMR) remains a significant barrier to achieving long-term graft survival in kidney transplantation, which results from alloantibody production from B lymphocytes and plasma cells. APRIL (A proliferation-inducing ligand) and BLyS (B lymphocyte stimulator) are critical survival factors for B lymphocytes and plasma cells. Here we describe the results of APRIL/BLyS blockade in a murine cAMR kidney transplant model. c57/B6 mice underwent kidney transplantation with Bm12 kidneys (minor MHC mismatch), a well-described model for chronic rejection where animals cannot make donor specific antibody but rather make antinuclear antibody (ANA). Following transplantation, animals received TACI-Ig (to block APRIL and BLyS) or no treatment. Animals were continued on treatment until harvest 4 weeks following transplant. Serum was analyzed for circulating anti-nuclear autoantibodies using HEp-2 indirect immunofluorescence. Spleen and transplanted kidneys were analyzed via H&E. ANA production was significantly decreased in APRIL/BLyS blockade treated animals (p<0.0001). No significant difference in autoantibody production was found between syngeneic transplant control (B6 to B6) and APRIL/BLyS blockade treated animals (p = 0.90). Additionally, disruption of splenic germinal center architecture was noted in the APRIL/BLyS blockade treated animals. Despite the significant decrease in autoantibody production and germinal center disruption, no significant difference in lymphocyte infiltration was noted in the transplanted kidney. APRIL/BLyS blockade resulted in a significant decrease of autoantibody production and disrupted splenic germinal center formation in a chronic kidney transplant model, however in this model no difference in kidney transplant pathology was seen, which may have to do with the absence of any T cell centric immunosuppression. Regardless, these findings suggest that APRIL/BLyS blockade may play a role in decreasing antibody formation long-term in kidney transplantation. Future investigations will use APRIL/BLyS blockade in conjunction with T lymphocyte depleting agents to determine its efficacy in chronic rejection.

APRIL/BLyS Blockade Reduces Donor-specific Antibodies in Allosensitized Mice.

BACKGROUND: Highly sensitized candidates on the transplant waitlist remain a significant challenge, as current desensitization protocols have variable success rates of donor-specific antibody (DSA) reduction. Therefore, improved therapies are needed. A proliferation-inducing ligand (APRIL) and B-lymphocyte stimulator (BLyS) are critical survival factors for B-lymphocytes and plasma cells, which are the primary sources of alloantibody production. We examined the effect of APRIL/BLyS blockade on DSA in a murine kidney transplant model as a possible novel desensitization strategy. METHODS: C57BL/6 mice were sensitized with intraperitoneal (IP) injections of 2 × 10 BALB/c splenocytes. Twenty-one days following sensitization, animals were treated with 100 µg of BLyS blockade (B-cell activating factor receptor-immunoglobulin) or APRIL/BLyS blockade (transmembrane activator and calcium modulator and cyclophilin ligand interactor-immunoglobulin), administered thrice weekly for an additional 21 days. Animals were then euthanized or randomized to kidney transplant with Control Ig, BLyS blockade, or APRIL/BLyS blockade. Animals were euthanized 7 days posttransplant. B-lymphocytes and DSA of BLyS blockade only or APRIL/BLyS blockade-treated mice were assessed by flow cytometry, immunohistochemistry, and enzyme-linked immunospot. RESULTS: APRIL/BLyS inhibition resulted in a significant reduction of DSA by flow crossmatch compared with controls (P < 0.01). APRIL/BLyS blockade also significantly depleted IgM- and IgG-secreting cells and B-lymphocyte populations compared to controls (P < 0.0001). APRIL/BLyS blockade in transplanted mice also resulted in decreased B-lymphocyte populations; however, no difference in rejection rates were seen between groups. CONCLUSIONS: APRIL/BLyS blockade with transmembrane activator and calcium modulator and cyclophilin ligand interactor-immunoglobulin significantly depleted B-lymphocytes and reduced DSA in this sensitized murine model. APRIL/BLyS inhibition may be a clinically useful desensitization strategy for sensitized transplant candidates.

Desensitization and treatment with APRIL/BLyS blockade in rodent kidney transplant model.

Alloantibody represents a significant barrier in kidney transplant through the sensitization of patients prior to transplant through antibody mediated rejection (ABMR). APRIL BLyS are critical survival factors for mature B lymphocytes plasma cells, the primary source of alloantibody. We examined the effect of APRIL/BLyS blockade via TACI-Ig (Transmembrane activator calcium modulator cyclophilin lig interactor-Immunoglobulin) in a preclinical rodent model as treatment for both desensitization ABMR. Lewis rats were sensitized with Brown Norway (BN) blood for 21 days. Following sensitization, animals were then sacrificed or romized into kidney transplant (G4, sensitized transplant control); desensitization with TACI-Ig followed by kidney transplant (G5, sensitized + pre-transplant TACI-Ig); kidney transplant with post-transplant TACI-Ig for 21 days (G6, sensitized + post-transplant TACI-Ig); desensitization with TACI-Ig followed by kidney transplant post-transplant TACI-Ig for 21 days (G7, sensitized + pre- post-transplant TACI-Ig). Animals were sacrificed on day 21 post-transplant tissues were analyzed using flow cytometry, IHC, ELISPOT, RT-PCR. Sensitized animals treated with APRIL/BLyS blockade demonstrated a significant decrease in marginal zone non-switched B lymphocyte populations (p<0.01). Antibody secreting cells were also significantly reduced in the sensitized APRIL/BLyS blockade treated group. Post-transplant APRIL/BLyS blockade treated animals were found to have significantly less C4d deposition less ABMR as defined by Banff classification when compared to groups receiving APRIL/BLyS blockade before transplant or both before after transplant (p<0.0001). The finding of worse ABMR in groups receiving APRIL/BLyS blockade before both before after transplant may indicate that B lymphocyte depletion in this setting also resulted in regulatory lymphocyte depletion resulting in a worse rejection. Data presented here demonstrates that the targeting of APRIL BLyS can significantly deplete mature B lymphocytes, antibody secreting cells, effectively decrease ABMR when given post-transplant in a sensitized animal model.

Complete B Cell Deficiency Reduces Allograft Inflammation and Intragraft Macrophages in a Rat Kidney Transplant Model.

BACKGROUND: Increasingly, it is being appreciated that B cells have broad roles beyond the humoral response and are able to contribute to and regulate inflammation. The specific role of B cells in the pathogenesis of early allograft inflammation remains unclear. METHODS: To address this question, we generated B cell-deficient (B) Lewis rats via clustered regularly interspaced short palindromic repeats (CRISPR) technology. In a full mismatch transplant model, kidneys from Brown Norway donors were transplanted into B Lewis recipients or wild type Lewis recipients. T cell-mediated rejection was attenuated with cyclosporine. RESULTS: Renal inflammation was reduced at 1 week after transplant (Banff scores for interstitial inflammation, microvascular inflammation, glomerulitis, and C4d) in allografts from B recipients. The reduction in interstitial inflammation was predominantly due to a decline in graft infiltrating macrophages. Intragraft T-cell numbers remained unchanged. In addition, B-cell deficiency was associated with increased T regulatory cells and reduced splenic T follicular helper cells at baseline; and significantly increased intragraft and splenic IL-10 mRNA levels after transplant. In vitro, B and wild type splenic T cells produced similar levels of IFN-γ in response to T cell-specific activation. CONCLUSIONS: B-cell deficiency in this model produced an anti-inflammatory phenotype with a shift toward regulatory T-cell populations, production of anti-inflammatory cytokines (IL-10), and a reduction in allograft inflammation. These findings define a role for B cells to influence the cell populations and mediators involved in the pathogenesis of early allograft inflammation.

Ki-67 is an independent predictor of metastasis and cause-specific mortality for prostate cancer patients treated on Radiation Therapy Oncology Group (RTOG) 94-08.

PURPOSE: The association of Ki-67 staining index (Ki67-SI) with overall survival (OS), disease-specific mortality (DSM), distant metastasis (DM), and biochemical failure (BF) was examined in men with favorable- to intermediate-risk prostate cancer receiving radiation therapy (RT) alone or with short-term androgen deprivation (ADT) in Radiation Therapy Oncology Group (RTOG) 94-08. METHODS AND MATERIALS: 468 patients (23.6%) on RTOG 94-08 had sufficient tissue for Ki67-SI analysis. The median follow-up time was 7.9 years. Ki67-SI was determined by immunohistochemistry and quantified manually and by image analysis. Correlative analysis versus clinical outcome was performed using the third quartile (≥Q3) cutpoint. A proportional hazards multivariable analysis (MVA) dichotomized covariates in accordance with trial stratification and randomization criteria. RESULTS: In MVAs adjusted for all treatment covariates, high Ki67-SI (≥Q3) was correlated with increased DSM (hazard ratio [HR] 2.48, P=.03), DM (HR 3.5, P=.002), and BF (HR 3.55, P<.0001). MVA revealed similar Ki67-associated hazard ratios in each separate treatment arm for DSM, DM, and BF; these reached significance only for DM in the RT-alone arm and for BF in both arms. Ki67-SI was not a significant predictor of intraprostatic recurrence assessed by repeated biopsy 2 years after treatment. Patients with a high or low Ki67-SI seemed to experience a similar relative benefit from the addition of ADT to radiation. CONCLUSIONS: High Ki67-SI independently predicts for increased DSM, DM, and protocol BF in primarily intermediate-risk prostate cancer patients treated with RT with or without ADT on RTOG 94-08 but does not predict for local recurrence or for increased relative benefit from ADT. This and prior studies lend support for the use of Ki67-SI as a stratification factor in future trials.

The role of p53 in radiation therapy outcomes for favorable-to-intermediate-risk prostate cancer.

PURPOSE: Some prostate cancers may have molecular alterations that render them less responsive to radiation therapy; identification of these alterations before treatment might allow improved treatment optimization. This study investigated whether p53, a potential molecular determinant, could predict long-term radiation therapy outcome in a restricted group of relatively favorable-risk prostate cancer patients treated uniformly with irradiation alone. METHODS AND MATERIALS: This study included 53 patients previously treated with radiotherapy for favorable-to-intermediate-risk prostate cancer. These patients were selected for relatively low pretreatment PSAs (< or =21 ng/mL) and Gleason scores (< or =7) to decrease the likelihood of nonlocalized disease, because disease localization was necessary to examine the efficacy of localized radiation therapy. The status of p53 was immunohistochemically assessed in paraffin-embedded pretreatment biopsy specimens, along with appropriate controls. This marker was selected based upon a usable mutation prevalence in early-stage prostate cancer and its potential linkage with radiation response via cell cycle, DNA repair, and cell death pathways. Correlation between p53 mutation and clinical outcome was analyzed in univariate and multivariate fashion and included conventional prognosticators, such as stage, grade, and PSA. Freedom from biochemical failure was determined using American Society for Therapeutic Radiology and Oncology criteria. Limitations of prior studies were potentially avoided by requiring adequate posttreatment follow-up (median follow-up in nonfailing patients of 5.1 years), as well as pretreatment PSA and Gleason scores that suggested localized disease, and uniformity of treatment. RESULTS: The total group of 53 favorable-to-intermediate-risk patients demonstrated an actuarial biochemical failure rate of 35% at 5 years. Forty percent of all specimens had a greater than 10% labeling index for p53 mutation, and actuarial biochemical control was found to strongly and independently correlate with p53 status. Patients with higher p53 labeling indices demonstrated significantly higher PSA failure rates (p < 0.001). In contrast, p53 status did not correlate with pretreatment PSA, grade, or tumor stage. Similarly, pretreatment PSA (log-rank 0.22), Gleason score (log-rank 0.93), and T stage (log-rank 0.15) were not prognostic for outcome in this group of patients selected for their relatively favorable clinical characteristics. CONCLUSIONS: (1) p53 status in pretreatment biopsies strongly predicted for long-term biochemical control after radiation therapy in favorable-to-intermediate-risk prostate cancer patients. (2) If validated in other independent clinical data sets, p53 status should be considered as a stratification factor in future clinical trials and could be useful in guiding treatment. Abnormal p53 status might favor surgical management, aggressive dose escalation, or p53-targeted therapy.