 SAN FRANCISCO, Sept. 21, 2021 PRNewswire -- Nektar Therapeutics NASDAQ: NKTR announced it has entered into a new oncology clinical collaboration with Merck KGaA, Darmstadt, Germany and Pfizer Inc. to evaluate the maintenance regimen of NKTR-255, Nektars interleukin-15 IL-15 receptor agonist, in combination with avelumab, a PD-L1 inhibitor, in patients with locally advanced or metastatic urothelial carcinoma UC in the Phase II JAVELIN Bladder Medley study. 