Synthesize a formal 250-word scientific abstract suitable for a peer-reviewed medical journal based on the following raw data points: Study Subject: Efficacy of Xenotransplantation of Porcine Kidneys in Primates; Sample Size: 20 primates; Control Group: 10 primates receiving human kidneys; Results: Experimental group showed 90% organ function retention after 6 months vs 70% in control; Complications: 3 instances of minor antibody rejection; Conclusion: Viable alternative to human donation. Ensure the abstract follows the structured format: Background, Methods, Results, and Conclusion.