3422836 SDGF schwannoma-derived growth factor 12 3422834 SDGF smooth muscle cell derived growth factor 2 3422837 SDGF SMC-derived growth factor 1 3422833 SDGF spleen derived growth factor 1 3422832 SDGF stromally derived growth factor 1 3422831 SDGF sucrose density gradient fractionation 1 3422835 SDGF Sudden drop in graft function 1