An In Vivo Immunofluorescence Localization Method to Study Antibody Biodistribution

Following anesthetization as described in the text protocol, prepare for the tail vein inoculation of the antibody solutions. Disinfect the tail of the animal by wiping three times with an alcohol wipe. Dilate the tail veins by warming with a heat pad for approximately 30 seconds; avoid heating the entire animal. Using a 27-gauge tail vane catheter insert the butterfly needle into one of the two lateral tail veins.

Visualize blood backflow into the catheter to ensure that the needle is properly placed so that the solutions will fully enter the animal versus being captured in the tail.

Use a piece of surgical tape to carefully fix the tail with the inserted needle to the stage. Flush the catheter with 25 microliters of sterile phosphate-buffered saline. Then, inject the antibody solution into the catheter using insulin syringes. Flush the catheter once again with 25 microliters of sterile PBS. Remove the needle from the tail, and apply pressure to stop any bleeding.

Perform humane euthanasia of the mouse, as described in the text protocol, and lay the mouse in the supine position. Use surgical scissors and forceps to excise tumor tissues. Use forceps to grasp only the outer layer of skin between the set of mammary glands closest to the tail, and to make a small incision with a pair of surgical scissors. Introduce the closed scissors into the cut, and slowly open the tip to carefully separate the skin from the underlying abdominal wall membrane, keeping it intact.

Make a vertical incision up the abdomen, continuing to separate the skin from the inner membrane. Between the third and fourth mammary glands, make a horizontal cut across the abdomen, to allow retraction of the skin and visualization of the mammary glands. Grasping each tumor or normal gland with forceps, carefully trim away the attached skin using surgical scissors.

Place excised tissues into tissue disposable base molds that are pre-labeled and filled with optimal cutting temperature embedding medium. Quickly freeze the molds by placement on dry ice. In order to study off-target delivery, excise other tissues or organs of interest. Using a cryostat, section frozen tissue blocks at 10-micron thickness, and place adjacent sections onto pre-labeled adhesion glass slides.

Rinse frozen tissue slides with room temperature PBS for 5 minutes to remove the embedding medium. Demarcate tissue sections with a hydrophobic barrier pen to reduce the volume of solutions needed during staining. Fix the tissue sections with 4% paraformaldehyde solution for 5 minutes. After rinsing the slides in PBS for 5 minutes, permeabilize tissue sections with 0.5% Triton X-100 in PBS for 15 minutes. Rinse the slides again in PBS for 5 minutes.

Block the tissues with PBS containing 3% weight per volume bovine serum albumin and 5% volume per volume goat serum for 1 hour at room temperature. After rinsing the slides in PBS for 5 minutes, incubate the sections with record-keeping primary antibodies, such as a common nuclear, vascular, or cytoplasmic marker. Here, rat anti-mouse CD31 is used at a 1 to 100 dilution in the blocking solution. The slides with primary antibody are left overnight at 4 degrees Celsius, protected from dehydration on a slide tray.

Following incubation, rinse the slides in PBS for 5 minutes three times. Change the PBS each time. Incubate the slides with secondary antibodies to label the primary antibodies. For this application, visualize anti-B7-H3 antibody using AlexaFluor-546 conjugated goat anti-rabbit antibody, and visualize CD31 with AlexaFluor-488 goat anti-rat secondary antibody in blocking solution. Protect the slides from light and dehydration on a slide tray for 1 hour at room temperature.

After rinsing the slides in PBS, as before, apply one drop of the mounting medium into the center of the tissue slice. Carefully place a coverslip avoiding entrapment of air bubbles. Seal the edges of the coverslip with clear nail polish and allow to dry. Proceed with confocal microscopy imaging and quantitative image analysis, as described in the text protocol.