CRISPR knockout screening identifies combinatorial drug targets in pancreatic cancer and models cellular drug response

Predicting the response and identifying additional targets that will improve the efficacy of chemotherapy is a major goal in cancer research. Through large-scale in vivo and in vitro CRISPR knockout screens in pancreatic ductal adenocarcinoma cells, we identified genes whose genetic deletion or pharmacologic inhibition synergistically increase the cytotoxicity of MEK signaling inhibitors. Furthermore, we show that CRISPR viability scores combined with basal gene expression levels could model global cellular responses to the drug treatment. We develop drug response evaluation by in vivo CRISPR screening (DREBIC) method and validated its efficacy using large-scale experimental data from independent experiments. Comparative analyses demonstrate that DREBIC predicts drug response in cancer cells from a wide range of tissues with high accuracy and identifies therapeutic vulnerabilities of cancer-causing mutations to MEK inhibitors in various cancer types.

Predicting the response to chemotherapy is a major goal of cancer research. Here the authors use CRISPR knockout screens in pancreatic ductal adenocarcinoma cells to identify deletions synergistic with MEK inhibitors.

A propensity matched analysis of robotic, minimally invasive, and conventional mitral valve surgery

OBJECTIVES

Institutional studies suggest robotic mitral surgery may be associated with superior outcomes. The objective of this study was to compare the outcomes of robotic, minimally invasive (mini), and conventional mitral surgery.

METHODS

A total of 2300 patients undergoing non-emergent isolated mitral valve operations from 2011 to 2016 were extracted from a regional Society of Thoracic Surgeons database. Patients were stratified by approach: robotic (n=372), mini (n=576) and conventional sternotomy (n=1352). To account for preoperative differences, robotic cases were propensity score matched (1:1) to both conventional and mini approaches.

RESULTS

The robotic cases were well matched to the conventional (n=314) and mini (n=295) cases with no significant baseline differences. Rates of mitral repair were high in the robotic and mini cohorts (91%), but significantly lower with conventional (76%, P<0.0001) despite similar rates of degenerative disease. All procedural times were longest in the robotic cohort, including operative time (224 vs 168 min conventional, 222 vs 180 min mini; all P<0.0001). The robotic approach had comparable outcomes to the conventional approach except there were fewer discharges to a facility (7% vs 15%, P=0.001) and 1 less day in the hospital (P<0.0001). However, compared with the mini approach, the robotic approach had more transfusions (15% vs 5%, P<0.0001), higher atrial fibrillation rates (26% vs 18%, P=0.01), and 1 day longer average hospital stay (P=0.02).

CONCLUSION

Despite longer procedural times, robotic and mini patients had similar complication rates with higher repair rates and shorter length of stay metrics compared with conventional surgery. However, the robotic approach was associated with higher atrial fibrillation rates, more transfusions and longer postoperative stays compared with minimally invasive approach.

Neoadjuvant Chemotherapy Is Associated with Lower Lymph Node Counts in Colon Cancer

Adequate lymphadenectomy is associated with improved survival in patients who undergo oncologic resection of colorectal cancer and has been identified as a quality metric. Neoadjuvant chemotherapy has been found to be associated with collection of <12 lymph nodes in patients with rectal cancer. The purpose of this study was to evaluate patient and operative risk factors for inadequate lymph node retrieval during oncologic colectomy. The 2014 American College of Surgeons National Surgical Quality Improvement Program Participant Use File data set for oncologic colectomy (n = 9077) was analyzed. Patient- and operation-related factors were assessed by univariate and multivariate regression analyses to determine factors associated with the number of lymph nodes collected. Adequate lymphadenectomy was defined by collection of >12 lymph nodes. Of 9077 patients with a diagnosis of colon cancer who underwent colectomy, a minimum of 12 lymph nodes was harvested in 7897 (87%). Significant factors independently associated with inadequate lymphadenectomy included preoperative chemotherapy, emergent surgery, and T1 tumors (all P < 0.05). A large majority of patients who undergo colectomy for colon cancer have at least 12 lymph nodes collected. Preoperative chemotherapy is a major risk factor for inadequate lymph node retrieval. Recognition of factors associated with inadequate lymphadenectomy may improve colectomy lymph node yield and survival in patients with colon cancer.

Neoadjuvant Chemotherapy is Associated with Lower Lymph Node Counts in Colon Cancer

Adequate lymphadenectomy is associated with improved survival in patients who undergo oncologic resection of colorectal cancer and has been identified as a quality metric. Neoadjuvant chemotherapy has been found to be associated with collection of <12 lymph nodes in patients with rectal cancer. The purpose of this study was to evaluate patient and operative risk factors for inadequate lymph node retrieval during oncologic colectomy. The 2014 American College of Surgeons National Surgical Quality Improvement Program Participant Use File data set for oncologic colectomy (n = 9077) was analyzed. Patient- and operation-related factors were assessed by univariate and multivariate regression analyses to determine factors associated with the number of lymph nodes collected. Adequate lymphadenectomy was defined by collection of >12 lymph nodes. Of 9077 patients with a diagnosis of colon cancer who underwent colectomy, a minimum of 12 lymph nodes was harvested in 7897 (87%). Significant factors independently associated with inadequate lymphadenectomy included preoperative chemotherapy, emergent surgery, and T1 tumors (all P < 0.05). A large majority of patients who undergo colectomy for colon cancer have at least 12 lymph nodes collected. Preoperative chemotherapy is a major risk factor for inadequate lymph node retrieval. Recognition of factors associated with inadequate lymphadenectomy may improve colectomy lymph node yield and survival in patients with colon cancer.

Open Surgical Incisions After Colorectal Surgery Improve Quality Metrics, But Do Patients Benefit?

BACKGROUND

Surgical site infection is a frequent cause of morbidity after colorectal resection and is a quality measure for hospitals and surgeons. In an effort to reduce the risk of postoperative infections, many wounds are left open at the time of surgery for secondary or delayed primary wound closure.

OBJECTIVE

The purpose of this study was to evaluate the impact of delayed wound closure on the rate of surgical infections and resource use.

DESIGN

This retrospective propensity-matched study compared colorectal surgery patients with wounds left open with a cohort of patients with primary skin closure.

SETTINGS

The American College of Surgeons National Quality Improvement Program Participant Use file for 2014 was queried.

PATIENTS

A total of 50,212 patients who underwent elective or emergent colectomy, proctectomy, and stoma creation were included.

MAIN OUTCOME MEASURES

Rates of postoperative infections and discharge to medical facilities were measured.

RESULTS

Surgical wounds were left open in 2.9% of colorectal cases (n = 1466). Patients with skin left open were broadly higher risk, as evidenced by a significantly higher median estimated probability of 30-day mortality (3.40% vs 0.45%; p < 0.0001). After propensity matching (n = 1382 per group), there were no significant differences between baseline characteristics. Within the matched cohort, there were no differences in the rates of 30-day mortality, deep or organ space infection, or sepsis (all p > 0.05). Resource use was higher for patients with incisions left open, including longer length of stay (11 vs 10 d; p = 0.006) and higher rates of discharge to a facility (34% vs 27%; p < 0.001).

LIMITATIONS

This study was limited by its retrospective design and a large data set with a bias toward academic institutions.

CONCLUSIONS

In a well-matched colorectal cohort, secondary or delayed wound closure eliminates superficial surgical infections, but there was no decrease in deep or organ space infections. In addition, attention should be given to the possibility for increased resource use associated with open surgical incisions. See Video Abstract at http://links.lww.com/DCR/A560.

Patient Reported Outcomes 10 years After Roux-en-Y Gastric Bypass

BACKGROUND

Following weight-loss surgery, patients who failed to achieve or sustain weight loss have nevertheless reported high satisfaction with their long-term bariatric experience. Understanding this phenomenon better will likely improve patients' experiences.

OBJECTIVE

The purpose of this study was to explore patients' long-term experiences following bariatric surgery.

SETTING

A 604-bed academic health system in the USA.

METHODS

Participants rated satisfaction and shared spontaneous comments regarding their gastric bypass experience. A phenomenological mode of inquiry explored participants' experiences. Transcribed phrases were categorized and themes identified.

RESULTS

In a 2004 surgical cohort, with 55% (155/281) participation, 99% of participants rated bariatric experience satisfaction (mean score 8.4) and 74% (115/155) shared comments regarding experiences. Responses were categorized as positive (63% 72/115), neutral (25% 29/115), or negative (12% 14/115). Satisfaction, Appreciation, and Gratefulness emerged as themes from positive comments, with 8% (6/72) explicitly acknowledging amount of weight loss achieved. Twenty-five percent (18/72) spontaneously mentioned undergoing surgery again or recommending the procedure to others. Neutral comments contained the themes of Reflection, Acknowledgment, and Wistfulness. Themes of Dissatisfaction, Disappointment, and Regret emerged from negative comments. Forty-three percent (6/14) of negative comments remarked on regaining weight or not reaching goal weight. Twenty-one percent (3/14) of negative comments explicitly stated regret at having undergone surgery.

CONCLUSIONS

Participants readily shared comments regarding their gastric bypass experience. Exploring themes provided insight into patients' satisfaction with bariatric surgery even when weight-loss goals were not met and conversely substantial dissatisfaction even when weight loss occurred. This study underscores the importance of understanding the patients' long-term experience following bariatric surgery.

Ureteral stents increase risk of postoperative acute kidney injury following colorectal surgery

BACKGROUND

Ureteral stents are commonly placed before colorectal resection to assist in identification of ureters and prevent injury. Acute kidney injury (AKI) is a common cause of morbidity and increased cost following colorectal surgery. Although previously associated with reflex anuria, prophylactic stents have not been found to increase AKI. We sought to determine the impact of ureteral stents on the incidence of AKI following colorectal surgery.

METHODS

All patients undergoing colon or rectal resection at a single institution between 2005 and 2015 were reviewed using American College of Surgeons National Surgical Quality Improvement Program dataset. AKI was defined as a rise in serum creatinine to ≥ 1.5 times the preoperative value. Univariate and multivariate regression analyses were performed to identify independent predictors of AKI.

RESULTS

2910 patients underwent colorectal resection. Prophylactic ureteral stents were placed in 129 patients (4.6%). Postoperative AKI occurred in 335 (11.5%) patients during their hospitalization. The stent group demonstrated increased AKI incidence (32.6% vs. 10.5%; p < 0.0001) with bilateral having a higher rate than unilateral stents. Hospital costs were higher in the stent group ($23,629 vs. $16,091; p < 0.0001), and patients with bilateral stents had the highest costs. Multivariable logistic regression identified predictors of AKI after colorectal surgery including age, procedure duration, and ureteral stent placement.

CONCLUSIONS

Prophylactic ureteral stents independently increased AKI risk when placed prior to colorectal surgery. These data demonstrate increased morbidity and hospital costs related to usage of stents in colorectal surgery, indicating that placement should be limited to patients with highest potential benefit.

CD47 Blockade as an Adjuvant Immunotherapy for Resectable Pancreatic Cancer

Purpose: Patients with pancreatic ductal adenocarcinoma (PDAC) who undergo surgical resection and adjuvant chemotherapy have an expected survival of only 2 years due to disease recurrence, frequently in the liver. We investigated the role of liver macrophages in progression of PDAC micrometastases to identify adjuvant treatment strategies that could prolong survival.Experimental Design: A murine splenic injection model of hepatic micrometastatic PDAC was used with five patient-derived PDAC tumors. The impact of liver macrophages on tumor growth was assessed by (i) depleting mouse macrophages in nude mice with liposomal clodronate injection, and (ii) injecting tumor cells into nude versus NOD-scid-gamma mice. Immunohistochemistry and flow cytometry were used to measure CD47 ("don't eat me signal") expression on tumor cells and characterize macrophages in the tumor microenvironment. In vitro engulfment assays and mouse experiments were performed with CD47-blocking antibodies to assess macrophage engulfment of tumor cells, progression of micrometastases in the liver and mouse survival.Results:In vivo clodronate depletion experiments and NOD-scid-gamma mouse experiments demonstrated that liver macrophages suppress the progression of PDAC micrometastases. Five patient-derived PDAC cell lines expressed variable levels of CD47. In in vitro engulfment assays, CD47-blocking antibodies increased the efficiency of PDAC cell clearance by macrophages in a manner which correlated with CD47 receptor surface density. Treatment of mice with CD47-blocking antibodies resulted in increased time-to-progression of metastatic tumors and prolonged survival.Conclusions: These findings suggest that following surgical resection of PDAC, adjuvant immunotherapy with anti-CD47 antibody could lead to substantially improved outcomes for patients. Clin Cancer Res; 24(6); 1415-25. ©2017 AACR.

Risk Associated With Complications and Mortality After Urgent Surgery vs Elective and Emergency Surgery: Implications for Defining "Quality" and Reporting Outcomes for Urgent Surgery

Importance

Given the current climate of outcomes-driven quality reporting, it is critical to appropriately risk stratify patients using standardized metrics.

Objective

To elucidate the risk associated with urgent surgery on complications and mortality after general surgical procedures.

Design, Setting, and Participants

This retrospective review used the American College of Surgeons National Surgery Quality Improvement Program database to capture all general surgery cases performed at 435 hospitals nationwide between January 1, 2013, and December 31, 2013. Data analysis was performed from November 11, 2015, to February 16, 2017.

Exposures

Any operations coded as both nonelective and nonemergency were designated into a novel category titled urgent.

Main Outcomes and Measures

The primary outcome was 30-day mortality; secondary outcomes included 30-day rates of complications, reoperation, and readmission in urgent cases compared with both elective and emergency cases.

Results

Of 173 643 patients undergoing general surgery (101 632 females and 72 011 males), 130 235 (75.0%) were categorized as elective, 22 592 (13.0%) as emergency, and 20 816 (12.0%) as nonelective and nonemergency. When controlling for standard American College of Surgeons National Surgery Quality Improvement Program preoperative risk factors, with elective surgery as the reference value, the 3 groups had significantly distinct odds ratios (ORs) of experiencing any complication (urgent surgery: OR, 1.38; 95% CI, 1.30-1.45; P < .001; and emergency surgery: OR, 1.65; 95% CI, 1.55-1.76; P < .001) and of mortality (urgent surgery: OR, 2.32; 95% CI, 2.00-2.68; P < .001; and emergency surgery: OR, 2.91; 95% CI, 2.48-3.41; P < .001). Surgical procedures performed urgently had a 12.3% rate of morbidity (n = 2560) and a 2.3% rate of mortality (n = 471).

Conclusions and Relevance

This study highlights the need for improved risk stratification on the basis of urgency because operations performed urgently have distinct rates of morbidity and mortality compared with procedures performed either electively or emergently. Because we tie quality outcomes to reimbursement, such a category should improve predictive models and more accurately reflect the quality and value of care provided by surgeons who do not have traditional elective practices.

Neuroendocrine liver metastasis: The chance to be cured after liver surgery

BACKGROUND AND OBJECTIVE

Neuroendocrine liver metastasis tumors (NELM) are a heterogeneous group of neoplasms with varied histologic features and a wide range of clinical behaviors. We aimed to identify the fraction of patients cured after liver surgery for NELM.

METHODS

Cure fraction models were used to analyze 376 patients who underwent hepatectomy with curative intent for NELM.

RESULTS

The median and 5-year disease-free survival (DFS) were 4.5 years and 46%, respectively. The probability of being cured from NELM by liver surgery was 44%; the time to cure was 5.1 years. In a multivariable cure model, type of neuroendocrine tumor (NET), grade of tumor differentiation, and rate of liver involvement resulted as independent predictors of cure. The cure fraction for patients with well differentiated NELM from gastrointestinal NET or a functional pancreatic NET, and with <50% of liver-involvement was 95%. Patients who had moderately/poorly differentiated NELM from a non-functional pancreatic NET, and with <50% of liver-involvement was 43%. In the presence of all the three unfavorable prognostic factors (nonfunctional PNET, liver involvement >50%, moderately/poorly differentiation), the cure fraction was 8%.

CONCLUSIONS

Statistical cure after surgery for NELM is possible, and allow for a more accurate prediction of long-term outcome among patients with NELM undergoing liver resection.

Access to Quaternary Care Surgery: Implications for Accountable Care Organizations

BACKGROUND

Accountable care organizations (ACOs) attempt to provide the most efficient and effective care to patients within a region. We hypothesized that patients who undergo surgery closer to home have improved survival due to proximity of preoperative and post-discharge care.

STUDY DESIGN

All (17,582) institutional American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) patients with a documented ZIP code and predicted risk, who underwent surgery at our institution (2005 to 2014), were evaluated. Google Maps calculated travel times, and patients were stratified by 1 hour of travel (local vs regional). Multivariable logistic regression and Cox proportional hazard models were used to evaluate the NSQIP risk-adjusted effects of travel time on operative morbidity, mortality, and long-term survival.

RESULTS

Median travel time was 65 minutes, with regional patients demonstrating significantly higher rates of ascites, hypertension, diabetes, disseminated cancer, >10% weight loss, higher American Society of Anesthesiologists (ASA) score, higher predicted risk of morbidity and mortality, and lower functional status (all p < 0.01). After adjusting for ACS NSQIP-predicted risk, travel time was not significantly associated with 30-day mortality (odds ratio [OR] 1.06; p = 0.42) or any major morbidities (all p > 0.05). However, survival analysis demonstrated that travel time is an independent predictor of long-term mortality (OR 1.24; p < 0.001).

CONCLUSIONS

Patients traveling farther for care at a quaternary center had higher rates of comorbidities and predicted risk of complications. Additionally, travel time predicts risk-adjusted long-term mortality, suggesting a major focus of ACOs will need to be integration of care at the periphery of their region.

Abstract C19: The role of resident liver macrophages in suppressing the progression of hepatic micrometastases from pancreatic ductal adenocarcinoma

Background: The majority of patients with localized pancreatic ductal adenocarcinoma (PDAC) die from metastatic disease, typically of the liver, despite a margin-negative (R0) resection. Therefore, these patients likely harbor occult metastatic disease in the liver at the time of surgery. In this study, we evaluated the role of resident liver macrophages in suppressing the progression of hepatic micrometastases using a murine model of micrometastatic PDAC with patient-derived xenografts (PDXs).

Methods and Results: Low-passage, patient-derived KRAS-mutant tumor cells expressing firefly luciferase were injected into the spleens of athymic nude mice resulting in liver metastases, followed by splenectomy to remove the primary tumor. Hepatic tumor burden and metastatic growth kinetics were evaluated by bioluminescent imaging on post-injection days 1, 2, 3, 7, and weekly thereafter. Each of the PDX tumors exhibited a decline in tumor burden over the initial days after injection followed by a period of quiescence with a reproducible, PDX-specific time to proliferative outgrowth ranging from 15 days to greater than 200 days. To assess the role of apoptosis in initial tumor cell clearance and suppression of outgrowth, mouse liver preparations were analyzed for expression of cleaved caspase-3 and cleaved PARP in tumor cells using flow cytometry. There was low expression of both apoptosis markers, suggesting that apoptosis is not a major cell-clearance mechanism. Athymic nude mice lack cell-mediated immunity but have functioning innate immunity. Because there is a large population of resident macrophages in the liver, we hypothesized that macrophages play an important role in the clearance and suppression of hepatic PDAC metastases. To test this, hepatic metastasis outgrowth was assessed following macrophage ablation with liposomal clodronate treatment of mice 48 hours prior to tumor cell injection. Following macrophage ablation, there was a trend toward less robust initial tumor cell clearance and a significantly decreased time to proliferative outgrowth compared with control (13 days vs 26 days, p=0.039). H&E sections demonstrated an abundance of hepatic macrophages surrounding tumor cells in the control group while this response was absent in the clodronate group. Splenic tumor cell injections were repeated using athymic nude mice vs NOD scid gamma (NSG) mice which lack both cell-mediated immunity as well as functional macrophages, dendritic cells, and NK cells. Initial tumor cell clearance was significantly reduced in the NSG mice vs nude mice (PDX 608: 35.6% vs 90.1% clearance at seven days, p&lt;0.001; PDX 366: 40.4% vs 76.3% clearance at seven days, p=0.024). Average relative hepatic bioluminescence at 21 days was significantly increased for PDX 608 in the NSG mice (14.7 vs 0.355, p=0.014) and there was a trend toward increase for PDX 366 (3.07 vs 0.025, p=0.065).

Conclusions: In a preclinical model of hepatic micrometastatic PDAC, resident liver macrophages are implicated in the initial clearance and the suppression of proliferation of tumor cells. Further investigation of the interaction of resident hepatic macrophages and micrometastatic PDAC cells may lead to novel strategies for therapy.

Citation Format: Alex D. Michaels, Timothy E. Newhook, James M. Lindberg, Sara J. Adair, Sarbajeet Nagdas, Matthew G. Mullen, Edward B. Stelow, J. Thomas Parsons, Todd W. Bauer. The role of resident liver macrophages in suppressing the progression of hepatic micrometastases from pancreatic ductal adenocarcinoma. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr C19.

Declining Operative Experience for Junior-Level Residents: Is This an Unintended Consequence of Minimally Invasive Surgery?

INTRODUCTION

Our group has previously demonstrated an upward shift from junior to senior resident participation in common general surgery operations, traditionally performed by junior-level residents. The objective of this study was to evaluate if this trend would correct over time. We hypothesized that junior resident case volume would improve.

METHODS

A sample of essential laparoscopic and open general surgery procedures (appendectomy, inguinal herniorrhaphy, cholecystectomy, and partial colectomy) was chosen for analysis. The American College of Surgeons National Surgical Quality Improvement Program Participant Use Files were queried for these procedures between 2005 and 2012. Cases were stratified by participating resident post-graduate year with "junior resident" defined as post-graduate year1-3. Logistic regression was performed to determine change in junior resident participation for each type of procedure over time.

RESULTS

A total of 185,335 cases were included in the study. For 3 of the operations we considered, the prevalence of laparoscopic surgery increased from 2005-2012 (all p < 0.001). Cholecystectomy was an exception, which showed an unchanged proportion of cases performed laparoscopically across the study period (p = 0.119). Junior resident participation decreased by 4.5%/y (p < 0.001) for laparoscopic procedures and by 6.2%/y (p < 0.001) for open procedures. The proportion of laparoscopic surgeries performed by junior-level residents decreased for appendectomy by 2.6%/y (p < 0.001) and cholecystectomy by 6.1%/y (p < 0.001), whereas it was unchanged for inguinal herniorrhaphy (p = 0.75) and increased for partial colectomy by 3.9%/y (p = 0.003). A decline in junior resident participation was seen for all open surgeries, with appendectomy decreasing by 9.4%/y (p < 0.001), cholecystectomy by 4.1%/y (p < 0.002), inguinal herniorrhaphy by 10%/y (p < 0.001) and partial colectomy by 2.9%/y (p < 0.004).

CONCLUSIONS

Along with the proliferation of laparoscopy for common general surgical procedures there has been a concomitant reduction in the participation of junior-level residents. As previously thought, familiarity with laparoscopy has not translated to redistribution of basic operations from senior to junior residents. This trend has significant implications for general surgery resident education.

The Progression of Cholelithiasis to Gallstone Ileus: Do Large Gallstones Warrant Surgery?

Gallstone ileus is a rare cause of small bowel obstruction, classically occurring in patients with recurrent cholecystitis. The incidence of biliary enteric fistula and gallstone ileus in patients with large, asymptomatic gallstones is not known. We report a case of gallstone ileus, which occurred in the setting of a large, asymptomatic gallstone. This case suggests that large gallstones may warrant cholecystectomy, even in asymptomatic patients.

Ileal J-Pouch Volvulus Following Total Proctocolectomy for Ulcerative Colitis

Total proctocolectomy with ileal pouch-anal anastomosis (IPAA) allows restoration of continence in select patients with ulcerative colitis but is associated with significant morbidity. Well-known complications following IPAA include pouchitis, anastomotic leak, and small bowel obstruction. Obstruction secondary to ileal pouch volvulus is exceedingly rare. We report a case of ileal pouch volvulus, which occurred secondary to internal hernia. Radiographic and endoscopic identification of volvulus allowed for early operative management and pouch salvage.

Plasmapheresis followed by intravenous immunoglobulin in presensitized patients awaiting thoracic organ transplantation

Four highly sensitized patients awaiting thoracic organ transplantation were treated immediately preceding transplantation with 1 plasmapheresis and infusion of high dose intravenous immunoglobulin (IVIG). All 4 underwent successful surgery and have had minor to no rejection episodes over a range from 5 1/2 to 12 months. All panel reactive antibodies (PRA) were dithiotheitol (DTT) resistant, and 1 patient had IgG specific alloantibodies to a donor alloantigen. All 4 patients had positive donor cross matches prior to transplantation, and 3 of the 4 patients remained PRA negative for up to 9 months after allografting. Possible mechanisms of this therapy include inhibition of proliferating alloreactive B cells or suppression by antiidiotypic antibodies. Further study is warranted.