Crystals of pembrolizumab and structurally similar anti-PD-1 monoclonal antibodies are provided, as well as methods of producing such crystals, and uses of compositions comprising such antibody crystals, e.g. in treatment of cancers. The present invention satisfies these needs and more by providing pembrolizumab crystals and a method producing pembrolizumab crystals. One embodiment of the method of the invention produces crystals suitable for X-ray diffraction, and the inventors herein used such crystals to solve the three-dimensional structure of pembrolizumab to 2.3 A resolution.
