Basicly I'm wanting to make a cultist leader, possibly cleric, that uses the explosive runes technique in melee range. I'm hoping to use spell immunity to pull it off, but I'm not sure if the rules allow for that. I have all the story elements worked out, but i don't want to flex the rules too hard, and I like my players to be able to do anything I can. So I would really like to stay within the confines of the printed text and make this work. Any thoughts/or suggestions would be helpful.
P.S. the backup plan is the leadership feat, with suicide bombers.
It seems like it should work, since explosive runes allows for spell resistance and is of 4th level or lower. Note that Explosive Runes though is not on the cleric spell list unless you have the Rune domain, so a cleric wouldn't be able to cast the spell himself w/o that domain. However, a cleric could cast Spell Immunity on a wizard, who could proceed to cast Explosive Runes in melee if you wish.
Also, as for your backup, I think summon monster would work better with suicide bomber types than followers. Remember that causing the death of your followers negatively impacts your Leadership score.