Added a ImmunityExtension

Source/Genes/Diseases/Defs/ImmunityAgainstGenesExtension.cs

@@ -0,0 +1,19 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Verse;
+
+namespace RJW_Genes
+{
+    public class ImmunityAgainstGenesExtension : DefModExtension
+    {
+        /// <summary>
+        /// A list of the exact defnames of disease-genes that this extension will make immune against.
+        /// Must perfectly match!
+        /// </summary>
+        public List<string> givesImmunityAgainst;
+    }
+
+}